Phẫu thuật đầu gối pps

Vol 7, No 5, September/October 1999 311 Patients who have undergone total knee arthroplasties are enjoying prolonged success of the procedure well into the second decade, with prosthetic survivorship in excess of 90% at 10 to 15 years. Despite these predictable results, a number of complications continue to plague patient and surgeon alike. These fall into three major groups: extensor mechanism complications, other mechanical complications, and regional or systemic complications. Understanding the incidence and etiology of these problems enhances the surgeonÕs ability to avoid them during the primary surgical procedure. With careful assessment of the symptomatic knee and an understanding of the effectiveness of salvage procedures, one can generally achieve a satisfactory result. Extensor Mechanism Complications Over the past three decades, the incidence of extensor mechanism complications has decreased from approximately 12% to 1.5% as a result of design modifications, technical advancements in attaining proper rotational and axial alignment of the individual components, and improvements in soft-tissue bal- ancing. 1-3 Nonetheless, the patellofemoral joint remains the most common source of pain and dysfunction after total knee arthroplasty. Patel- lofemoral instability, component dissociation or loosening, patellar fracture, residual anterior knee pain, component wear, osteonecrosis, patellar Òclunk,Ó and patellar tendon rupture account for up to 50% of secondary surgical procedures after total knee arthroplasty. 1,2 Patellofemoral Instability Patellar instability is the most common reason for secondary surgery after total knee arthroplasty. The reported incidence of patellar maltracking (tilting, subluxation, or dislocation) varies from 0.5% to as high as 29%. 1,3 Patellar maltracking may be related to prosthetic design, extensor mechanism imbalance, asymmetric patellar resection, malrotation of the femoral or tibial component, or patellar malpositioning. Component design is important for stable patellar tracking. To accommodate either a resurfaced or a nonresurfaced patella, the femoral component should ideally have a broad trochlear groove that extends proximally to accommodate the patella in full extension. The trochlea should be directed toward the lateral side to engage the patella early in flexion. Dis- tally, patellar tracking is enhanced when the trochlear groove is nar- rowed and deepened to contain the patella, limiting lateral subluxation in flexion. 4 Patellar views of the implant will display patellar component subluxation (Fig. 1). Theiss Dr. Lonner is Assistant Professor, Department of Orthopaedic Surgery, University of Penn- sylvania School of Medicine, Philadelphia. Dr. Lotke is Professor of Orthopaedic Surgery, University of Pennsylvania School of Medicine. Reprint requests: Dr. Lonner, Department of Orthopaedic Surgery, Hospital of the Univer- sity of Pennsylvania, 2 Silverstein, 3400 Spruce Street, Philadelphia, PA 19104. The authors or the departments with which they are affiliated have received something of value from a commercial or other party related directly or indirectly to the subject of this arti- cle. Copyright 1999 by the American Academy of Orthopaedic Surgeons. Abstract Aseptic complications after total knee arthroplasty are occurring less frequently than they did one or two decades ago. This is related in part to technical advancements, design improvements, and changes in perioperative management. Extensor mechanism dysfunction is the most frequent complication and the most commonly cited reason for secondary surgery after total knee arthroplasty. Mechanical wear, tibiofemoral instability, periprosthetic fracture, thromboembolic disease, compromised wound healing, neurovascular problems, and stiffness are less common, but nevertheless troublesome, sources of dysfunction after total knee arthroplasty. Complications compromise outcomes, and the most effective way of dealing with complications is prevention. J Am Acad Orthop Surg 1999;7:311-324 Aseptic Complications After Total Knee Arthroplasty Jess H. Lonner, MD, and Paul A. Lotke, MD et al 5 evaluated the data on total knee arthroplasties performed with implants of two different designs and found that the results were comparable except for the incidence of postoperative patellofemoral complications (10% for one design and 0.7% for the other). They attributed this disparity to the striking differences in femoral component morphology between the two designs. Patellar component design (e.g., dome-shaped buttons, ÒMexican hatÓÐlike buttons, and asymmetric components), medialization of the component to approximate the anatomic center axis, 6 the accuracy and extent of patellar bone resection, and restoration of patellar thickness may all affect patellar tracking. Excessive resection of the patella so that the remaining thickness is less than 10 to 15 mm may predispose it to fracture; insufficient resection may limit flexion and contribute to maltracking. 7 Proper tracking requires a normal Q angle, which is affected by the axial and rotational alignment of the femur and tibia. An excessive Q angle may result from medialization of the tibial tray, excessive valgus alignment of components, or internal rotation of either component. Patellofemoral maltracking may also result from soft-tissue imbalance if the lateral retinaculum is contracted or the medial retinacular sleeve is lax. Correct axial femoral component alignment, perpendicular to the mechanical axis, is paramount to prevention of patellar maltracking. The femoral component should also be implanted with enough external rotation to establish a rec- tangular flexion gap and to facili- tate patellar tracking. In addition, it should be appropriately sized in the anteroposterior dimension to avoid ÒoverstuffingÓ the patellofemoral compartment. A variety of methods have been developed for determining the appropriate rotational alignment of the femoral component (Fig. 2). 8 Using the posterior femoral condyles as a reference, the examiner should assess the knee for severe deformity or condylar hypoplasia. In the presence of severe valgus deformity, deficiency of the posterior lateral femoral condyle may erroneously place the cutting jig in relative internal rotation. Proper rotation of the tibial component, so that its center is in line with the medial third of the tibial tubercle, and avoidance of medialization of the tibial component will enhance patellar tracking (Fig. 3). Patellar tracking is most accurate- ly assessed with the tourniquet deflated, to eliminate the binding effect of the tourniquet on the quadriceps. Without closing of the medial retinaculum or forcing of the patella medially (Òthe rule of no thumbsÓ), the patella should track congruently within the trochlear groove without tilting or subluxat- ing. If the patella tilts or subluxates, a lateral retinacular release should be performed. If patellar subluxation still occurs, rotation, alignment, patellar composite thickness, and button position should be evaluated. Treatment of patellar maltracking is based on the cause of the instability. Nonsurgical treatments for patellar subluxation or dislocation are generally unsuccessful. Surgery must be directed at the underlying cause of the problem. In the absence of component malpositioning, a lateral retinacular release may be all that is necessary to improve patellar tracking. A lateral retinacular release is performed from the inside out in an attempt to preserve the blood supply of the skin flap as well as the lateral superior genicular vessels. Distal to the vessels, the lateral retinaculum is released in a direc- tion perpendicular to the joint line. Proximally, an oblique limb is directed 45 degrees anteriorly, relieving lateral traction by the ilio- tibial band in flexion. 9 Distal realignment involving tibial tubercle osteotomy has been advocated, particularly when an excessive Q angle is present. 10 However, when there is significant component malalignment, tubercle osteotomy is less effective than component revision. Aseptic Complications After Total Knee Arthroplasty Journal of the American Academy of Orthopaedic Surgeons 312 Fig. 1 Patellar view showing patellar subluxation and tilt. Note the asymmetric patellar osteotomy. Fig. 2 Four reference lines used in determining femoral component external rotation: AP = anteroposterior axis; PCA = posterior condylar axis; TEA = transepicondylar axis; TFG = tensioned flexion gap. Gener- ally, a balanced flexion gap will be created by resecting the posterior femoral condyles parallel to the TEA, perpendicular to the AP axis, 3 degrees externally rotated from the PCA, or parallel to the proximal tibia with the balanced collateral ligaments tensioned (as reflected by the TFG). Medial PCA Lateral TEA AP 3° TFG Patellar Fracture Patellar fracture after total knee arthroplasty has a variety of causes, including abnormal stress concen- trations, osteonecrosis, and patella baja. The patella is susceptible to failure when the bone has been weakened and high stresses are applied. Direct trauma to the patella after total knee arthroplasty is uncommon. Compressive loads across the patellofemoral articulation approach four to seven times body weight in certain activities, such as squatting and stair descent. Furthermore, when the transition zone between the trochlear region and the condylar region of the femoral component is abrupt, the localized stress concentration can be quite severe. Overstuffing the patellofemoral joint with an oversized femoral component, an anteriorly offset femoral component, or a femoral component placed in excessive extension can also overload the patella. A similar phenomenon may be seen with insufficient resection of the patella or use of a thick button. Excessive patellar resection can predispose to patellar fracture as well. Reuben et al 7 have demon- strated that a residual patellar thickness of less than 15 mm can substantially increase anterior patellar strain. Osteonecrosis of the patella may lead to late fracture and fragmenta- tion of the patella (Fig. 4). Anatomic studies of patellar blood supply have mapped out an extensive sys- tem of both extraosseous and intraosseous arterial systems. There are contributions from all the genicular vessels (Fig. 5). Each of these vessels is potentially at risk during the surgical approach, soft-tissue dissection, and subsequent patellar resurfacing. The standard medial parapatellar arthrotomy will divide the superior and inferior genicular arteries as well as the descending genicular artery. Additionally, the lateral inferior genicular artery is commonly sacrificed during lateral meniscectomy. When a lateral retinacular release is subsequently performed, the lateral superior genicular artery is at risk, particularly when not dissected free and protected. Aggressive resection of the infrapatellar fat pad can theoretically compromise the traversing branches that supply the inferior pole of the patella. However, this has not re- sulted in an obvious decrease in patellar perfusion. 11 Diminished patellar vascularity has been observed acutely on technetium bone scans, but follow-up studies suggest that patellar revascularization may occur as early as 60 days after the surgical procedure. 12 Elevation of the tibiofemoral joint line as a result of proximal femoral resection and posterior cruciate ligament release will cause relative patella baja. This creates a nonanatomic patellofemoral articulation, which may result in patellar impingement on the tibial insert in late flexion and ultimately in patellar fracture. Con- sidering the proximal shift in the joint line seen with standard posteriorly stabilized total knee arthroplasties, it has been postulated that there may be a higher risk of patellar fracture with these implants. 13 Treatment of patellar fractures is dependent on fracture pattern, loca- tion, remaining bone stock, integrity of the component-cement-bone interface, and competence of the extensor mechanism. The classifi- cation by Goldberg et al 14 is helpful for planning appropriate intervention. Type I fractures are avulsion- type fractures, generally involving the periphery of the patella but not the implant, cement, or quadriceps mechanism. Type II fractures dis- rupt the cement-prosthesis interfaces or the quadriceps mechanism. Type III-A fractures involve the inferior pole of the patella with disrup- tion of the patellar ligament. Type III-B are nondisplaced fractures of the inferior pole of the patella with an intact patellar ligament. Type IV fractures are fracture-dislocations of the patella. Nonoperative treatment is preferred when fractures are nondisplaced. 14-16 Unfortunately, the defi- nition of displacement used in the literature has varied from 2 mm to 2 cm, and clinical experience in treating patellar fractures after total knee arthroplasty has generally been Jess H. Lonner, MD, and Paul A. Lotke, MD Vol 7, No 5, September/October 1999 313 Fig. 3 The appropriate technique for aligning the tibial component is to rotate it so that its center is in line with the medial third of the tibial tubercle. Fig. 4 Lateral radiograph of a knee after total knee arthroplasty. Note displaced fracture of the inferior pole of an osteo- necrotic patella. The patellar component had been removed 1 year earlier because of dissociation. anecdotal. Hozack et al 15 reviewed 21 patellar fractures after total knee arthroplasty. Nonoperative treatment of nondisplaced or minimally displaced fractures (6 to 8 weeks of cast immobilization) yielded satisfactory results. The results of surgical treatment were variable, but more predictable outcomes were associated with partial or complete patellectomy than with attempted open reduction and internal fixation. Goldberg et al 14 reported comparable results in their experience treating 36 patellar fractures after total knee arthroplasty. Type I fractures, which had been treated in a cast in extension, had satisfactory results. Unfortunately, fracture pat- terns categorized as types II, III-A, or IV generally had unsatisfactory outcomes despite surgical intervention and appropriate postoperative physical therapy. Windsor et al 16 noted that comminuted patellar fractures, regardless of the extent of fragment displacement, can be treated in a cylinder cast, unless there is compromise of the prosthesis-patella composite. In the latter scenario, a patellectomy has better results than attempted open reduction and internal fixation, which may predispose the patella to osteonecrosis or nonunion. Another option for these comminuted fractures is to remove the patellar component and allow healing of the comminuted bone fragments in a cast. Transverse fractures with displacement by more than 1 cm and/or an extensor lag greater than 30 degrees may be treated with cerclage tension- band wiring, provided the patellar component is intact and the native bone stock is adequate. Otherwise, patellectomy is preferable. 15 Displaced avulsion fractures of either the proximal or the distal pole of the patella with an intact patellar component and a viable patella can be stabilized with heavy nonabsorbable sutures passed through the quadriceps tendon or patellar tendon and secured to the patella through drill holes. To protect the repair, a checkrein-type figure-of- eight stitch may be tied over the anterior aspect of the extensor mechanism. After fixation, patellar tracking and component stability should be assessed. Postoperatively, passive knee motion may be allowed. Patellar Tendon Rupture Rupture of the patellar tendon after total knee arthroplasty is uncommon, occurring in 0.17% to 1.45% of cases. 2,17 This injury can be devastating for the patient, as the results of treatment are frequently suboptimal. The most common cause of extensor mechanism dis- ruption is intraoperative tendon avulsion off the tibial tubercle that occurs when excessive tension is used when trying to obtain adequate exposure. Late rupture may result from manipulation, distal tubercle realignment procedures, direct trauma, or impingement on the tibial insert. Considering the relatively poor results of treatment of this complication, even with surgical intervention, it is preferable to be extremely careful when handling the tendon at the time of primary arthroplasty. A knee with limited motion or intra- articular scarring, particularly when associated with patella baja, is at greater risk. When exposure is difficult, graduated extensile exposure is initiated with posteromedial dissection and external tibial rotation. If necessary, a modified quadriceps Aseptic Complications After Total Knee Arthroplasty Journal of the American Academy of Orthopaedic Surgeons 314 Fig. 5 Left, The peripatellar extraosseous anastomotic ring is composed of six arteries: descending genicular (DG), medial superior genicular (MSG), medial inferior genicular (MIG), lateral superior genicular (LSG), lateral inferior genicular (LIG), and anterior tibial recurrent (ATR). Right, The three intraosseous zones of patellar blood supply are the quadriceps tendon supply (QT) proximally, the midpatellar supply (MP), and the polar supply (P) distally. LSG LIG ATR DG MSG MIG QT MP P V-plasty, quadriceps snip, or tibial tubercle osteotomy should be considered to protect the patellar tendon insertion. In addition, a pin or drill bit may be inserted into the distal patellar tendon insertion to protect it from avulsing. Manipulation of a stiff knee under anesthesia may be complicated by rupture of the patellar tendon or supracondylar fracture of the femur. The risk of these complications can be reduced, in part, by performing manipulation within 6 weeks of arthroplasty. If distal ligament avulsions involve less than 30% of the tibial tubercle insertion, a primary repair of the medial capsuloretinacular sleeve should suffice, without any need for alteration in normal postoperative physical therapy. For complete avulsions, primary reat- tachment has been relatively unsuccessful, with a high incidence of rerupture and functional impair- ment. 17 Primary suture repair of attri- tional or traumatic ruptures is typi- cally ineffective. In general, there are two methods of patellar tendon reconstruction that may be effective in these circumstances. The deci- sion of which to use is influenced by the quality of the remaining native patellar bone stock. When there is adequate patellar bone stock, primary repair and augmen- tation with an autogenous semitendinosus graft is effective. With the technique modified from Cadambi and Engh 18 and Ecker et al, 19 the standard total knee incision can be used to harvest the semitendinosus, leaving its insertion point on the pes anserinus intact. The attached graft is then routed proximally along the medial aspect of the patellar tendon, passed trans- versely through the patella, and sutured back to its pes anserinus insertion. Postoperatively, the knee is immobilized in extension for 6 to 8 weeks before progressive rehabilitation is started. An extensor mechanism allograft can be considered when the patellar bone stock and soft tissue are deficient (Fig. 6). Emerson et al 20 reported satisfactory results with the use of an allograft quadriceps tendon, patella, patellar tendon, and tibial tubercle bone block. The allograft tibial tubercle is fitted into a trough in the tibial tubercle, placed so that the patella will be positioned appropriately with respect to the joint line, and is then secured with screws. The patella may or may not be resurfaced. The quadriceps component of the allograft is tensioned and secured to the host quadriceps tendon with nonabsorbable sutures. The graft should have a moderate amount of tension with the knee fully extended, allowing approximately 60 to 70 degrees of flexion against gravity. The native host tissues are sutured over the allograft to Jess H. Lonner, MD, and Paul A. Lotke, MD Vol 7, No 5, September/October 1999 315 Fig. 6 A, Lateral radiograph shows patella alta due to insufficiency of the patellar tendon after total knee arthroplasty. B, Intraoperative photograph of an implanted extensor mechanism allograft in a patient with patellar tendon rupture and inadequate patellar bone stock. The tibial trough is made after establishing the appropriate position of the patella relative to the joint line. The bone plug is secured with one or two cortical screws. The allograft is sutured peripherally to the remaining undersurface of the host extensor mechanism with nonabsorbable suture. The native tissues are then closed over the allograft. C, Postoperative lateral radiograph after reconstruction. The allograft patella was not resurfaced. A B C minimize the risk of soft-tissue slough and to promote healing. Postoperatively, passive range-of- motion exercises may begin immediately. Progressive rehabilitation should be initiated carefully. Al- though the 2-year results with this technique are encouraging, longer- term follow-up is necessary. 20 Soft-Tissue Impingement The Òpatellar clunk syndromeÓ occurs when a fibrous nodule or proliferative synovium forms at the insertion of the quadriceps tendon and impinges on the patella. 21 The symptoms include snapping, pain, crepitus, and sometimes secondary patellar instability. This condition occurs almost exclusively in patients with posteriorly stabilized implants. The fibrous nodule may lodge within the intercondylar notch of the femoral component in flexion and catch on the femoral component as the knee proceeds into extension, causing the charac- teristic symptoms. When a posteriorly stabilized knee prosthesis is used, the peripatellar synovium around the quadriceps tendon insertion should be excised (Fig. 7). The prosthesis design may also play a role in the development of patellar clunk syndrome. Newer femoral components have a lower box and a more posterior position of the femoral cam, which minimizes the risk of soft- tissue impingement within the box. Nonoperative treatment of early patellar clunk syndrome or retropatellar scarring should include a trial of anti-inflammatory medica- tions. Use of intra-articular corticosteroid injections after total knee arthroplasty is ill advised. In the event that nonoperative measures fail to adequately relieve the pa- tientÕs symptoms, arthroscopic debridement or arthrotomy with debridement and excision of hypertrophic tissue is recommended. Arthroscopic debridement is effective; however, care must be taken to avoid scratching the implants. Arthrotomy may be necessary if extremely dense peripatellar adhe- sions make arthroscopic visualiza- tion difficult. Patellar Component Wear and Loosening Patellar component wear is common, but loosening of the patellar component is uncommon, report- edly occurring in approximately 1% of cases. 1 Considering the high compressive shear stresses trans- mitted across the patellofemoral articulation, it is surprising that the incidence of loosening of patellar components is not higher. Risk factors for patellar component loosening or dissociation include deficient bone stock, component malpositioning, patellar maltracking, patellar osteonecrosis, asymmetric bone resection, altered joint line, osteoly- sis due to reaction to metal debris, failure of bone ingrowth in porous- coated designs, and obesity. Metal backing was introduced to help dissipate joint contact forces. Unfortunately, metal-backed implants commonly failed because of failure of bone ingrowth, delamination of the polyethylene from the metal backing, and rapid polyethylene wear, with subsequent metal-on-metal contact and generation of metallic debris. Aseptic Complications After Total Knee Arthroplasty Journal of the American Academy of Orthopaedic Surgeons 316 Fig. 7 A, Arthroscopic view shows hypertrophic synovium on the posterior aspect of the quadriceps tendon, impinging within the intercondylar housing of the femoral component beyond 70 degrees of flexion. B, Impingement of the scar was eliminated after arthroscopic excision of the hypertrophic tissue. A B Failure of the patellar component may present with a variety of symptoms, ranging from a painless effusion to retropatellar pain, click- ing, or instability. Radiographic findings may be subtle, although the outline of a dissociated patellar component may be visualized on a Merchant view, or thinning of the polyethylene may be seen. In cases of failure of a metal-backed component, the metal base plate may be seen articulating with the femoral component, or metallic stippling within the soft tissues (Òmetallic synovitisÓ) may be seen. Failed Patellar Component Revision of a failed patellar prosthesis can be difficult and must be individualized, depending on the remaining patellar bone stock and the condition of the articulating femoral component. If the native patellar bone stock is insufficient, either patellaplasty or patellectomy should be considered. Resurfacing of an inadequate patella may result in osteonecrosis or fracture. Isolated patellar component revision has yielded mixed results, with high complication rates. Berry and Rand 22 reported good or excellent results in 30 of 36 knees (83%) at follow-up 2 to 8 years after isolated patellar component revision. Nonetheless, complications were observed in 14 of 36 knees (39%). Failure of a metal- backed patellar component may result in burnishing or scoring of the femoral component, necessitating its revision as well. Thorough joint debridement to remove the metal- stained synovium and inspection of the implant-bone interfaces are necessary to ensure that significant oste- olysis or loosening has not occurred. Tibiofemoral Flexion Instability Equal flexion and extension spaces are critical to ensure stability and pre- vent postoperative subluxation. Tibiofemoral instability in flexion may occur in the immediate postoperative period, or it may have a delayed onset. There are several poten- tial causes of this problem, including excessive recession or delayed incompetence of the posterior cruciate ligament in cruciate-retaining knee implants, excessive resection of the posterior femoral condyles, asymme- try of the flexion space, incompetence of the medial collateral ligament, or overzealous release of soft-tissue restraints. Late polyethylene wear of the tibial insert may create further instability in flexion. Rupture of the extensor mechanism may result in posterior instability. Treatment of prosthetic knee-joint instability must be predicated on its origin. Sacrificing the posterior cruciate ligament will enlarge the flexion space, which does not routinely occur with cruciate retention. There- fore, the distal femoral osteotomy is usually made 2 to 3 mm more proximally relative to the trochlear groove. Resection of the distal femur to the level of the trochlear notch will create equal flexion and extension gaps in cruciate-substituting total knee arthroplasties. Although this may elevate the joint line by 2 to 4 mm in balanced posterior- substituting total knee arthroplasties, it is unavoidable; fortunately, it is generally well tolerated. When posterior cruciate ligament recession is necessary for placement of cruciate-retaining implants, one must carefully assess the integrity of the ligament at the termination of the procedure. Com- plete recession of the posterior cruciate ligament in the setting of severe varus or valgus deformity should not cause instability if a curved tibial insert is utilized. 23 However, rupture of an attenuated posterior cruciate ligament, as has been observed in patients with rheumatoid arthritis, may result in delayed instability in flexion. 24 Medial-lateral imbalance of the flexion space may result from either rotational malalignment of the femoral component or dynamic imbalance created by soft-tissue releases. A trapezoidal flexion space may cause asymmetric flexion instability. Femoral component rotation is an important factor. Soft- tissue releases must then be appropriately tailored so that the medial and lateral compartments are well balanced in flexion and extension. Residual medial-compartment instability may be treated with a constrained condylar-type implant, which will provide not only anteroposterior stability but also medial-lateral stability. If there is insufficiency of the medial collateral ligament, reconstruction may be necessary. A variety of techniques may be used, such as reconstruct- ing the ligament with a harvested looped semitendinosus autograft left intact at the pes anserinus insertion distally and then attached to the medial femoral epicondyle with a screw and soft-tissue washer. The reconstruction is augmented with a constrained condylar-type implant (Fig. 8). When delayed flexion instability occurs as a consequence of late posterior cruciate ligament failure or polyethylene wear, changing to a thicker insert may be adequate to address the problem. In that situation, an insert with sagittally curved topography should be utilized. If significant flexion instability persists, revision to a posterior stabilized implant is recommended. Wound Complications Compromised wound healing may increase the risk of infection and subsequent failure. The vascular anatomy of the knee, biomechanical factors, selection of surgical incisions, surgical technique, and Jess H. Lonner, MD, and Paul A. Lotke, MD Vol 7, No 5, September/October 1999 317 patient-related risk factors must all be considered when evaluating wound healing. Vascular Anatomy The blood supply to the soft tissues of the anterior aspect of the knee is relatively random and inconsistent, with contributions from the terminal branches of the peripatellar anastomotic arterial ring. Because there is no muscle beneath the skin and soft tissues of this region of the knee, perfusion is sparse. 25 The dermal plexus, which is composed of arterioles traveling within the subcutaneous fascia, is responsible for providing skin cir- culation. Therefore, elevation of skin flaps in the anterior aspect of the knee for exposure must be deep to the subcutaneous fascia to preserve the critical and often tenuous blood supply to the skin. Biomechanical Factors Biomechanical factors, such as surgical trauma, skin tension, ori- entation of skin incisions, early mobilization, and tissue oxygen tension, are important considera- tions as well. Making a surgical incision induces relative tissue hypoxia. The decline in oxygenation in the skin is dramatic, with a 67% decrease observed during the first postoperative day. By 8 days after surgery, the decrease in oxygenation is only 16%. 26 Considering the relative hypoxia of the lateral skin margin, a medial parapatellar skin incision is relatively undesirable, as it will create a large lateral skin flap with diminished oxygenation. 25 A midline incision is preferred for primary surgery; however, a preexisting surgical incision should be incorporated whenever Aseptic Complications After Total Knee Arthroplasty Journal of the American Academy of Orthopaedic Surgeons 318 A B E F C D Fig. 8 A and B, Anteroposterior and lateral radiographs of a patient with pain and instability due to malalignment of a total knee arthroplasty with laxity of the medial collateral ligament. Note the posterior tibiofemoral contact point. At the time of surgery, the medial collateral ligament was noted to be incompe- tent. C and D, Intraoperative photographs of reconstruction of the medial collateral ligament with the use of looped semitendinosus tendon autograft. E and F, Postoperative radiographs show revised total knee components and medial collateral ligament reconstruction. possible. If that is not feasible, the new incision should be parallel to the existing one, producing a bipedi- cle flap; the ratio between the width between incisions and the length of incisions should be more than 1:4. 27 Short peripatellar incisions may usually be ignored, particularly when they are more than a decade old. Prior transverse incisions may be crossed with longitudinal incisions without concern for devitalization. In the presence of multiple surgical scars, it is preferable to use the longest and/or most lateral incision to avoid a large lateral skin flap that may have a compromised vascular supply. A muscle flap or soft-tissue expander may be needed for patients with atrophic skin or multiple adher- ent broad scars. 25 Postoperative hemarthrosis or hematoma formation may cause wound problems by increasing tension. If a hemarthrosis is large, causes pain, and interferes with range of motion or if it compromises skin viability, early evacuation is prudent. Range-of-motion exercises should be delayed until the wound is stable. The same is true for a large subcutaneous hematoma, which may compromise the viability of the skin. In morbidly obese patients, closure of knee incisions with retention sutures may be helpful to minimize subcutaneous dead space. Patient Risk Factors Local and systemic factors known to inhibit wound healing include vasoconstriction due to nicotine use, atrophy of the skin, previous irradia- tion of tissue, and thermal or chemi- cal burns. Obesity may predispose to wound healing problems as well; this may be related to overzealous retraction, fat necrosis, or residual dead space. Diabetes mellitus may alter collagen synthesis and decrease the tensile strength of scar tissue. Corticosteroids decrease fibroblast proliferation, which is a necessary component of wound healing. It is unclear whether the increased rate of deep wound infections in patients with rheumatoid arthritis is related to problematic wound healing or the prolonged use of corticosteroids. Perioperative use of drugs such as methotrexate and malnutrition may further compromise wound healing. Nutritional supplementation in patients who have a serum albumin level less than 3.5 g/dL and a total lymphocyte count of less than 1,500/mm 3 may decrease the incidence of complications related to wound healing. Wound drainage beyond the first several days after surgery may increase the risk of infection. Taking cultures of the drainage is not advisable; these will often yield normal skin flora, and continuing prophy- lactic antibiotics longer than 24 hours is generally not necessary. Drainage will usually stop after immobilization of the limb for 24 to 48 hours; if not, the patient should undergo reoperation for explo- ration, deep culture, irrigation, and meticulous wound reclosure. Knee- motion exercises may be resumed once the wound is stable. If deep cultures are positive, parenteral antibiotic therapy should be continued for at least 6 weeks. Otherwise, antibiotics may be discontinued. Full-thickness skin necrosis must be treated aggressively to avoid deep infection. Salvage is predictable with debridement and cover- age with a rotational gastrocnemius flap, provided the procedure is performed expeditiously. 28 Failures may be inevitable if treatment is delayed and necrosis of the flap results in contamination of the knee. Stiffness There is a subset of patients who fail to regain the motion that one would expect in the initial postoperative period. The most important factor in predicting postoperative motion is the preoperative arc of motion. In the immediately postoperative period, limited recovery of motion is most commonly related to post- surgical pain. Patient-controlled analgesia or continuous epidural analgesia for 48 hours postoperatively is commonly utilized to ensure adequate pain relief and allow immediate motion. The effi- cacy of continuous-passive-motion machines continues to be debated. It is difficult to quantify the rate at which knee motion should improve, although the rate should be more rapid in the initial 2 to 4 weeks and then slower for the subsequent 6 weeks. Paradoxically, overzealous therapy or activity may cause stiffness due to pain and inflammation. Other common causes include arthrofibrosis, low-grade infection, excessive soft-tissue tension due to improper releases or overstuffing of the joint, a tight posterior cruciate ligament, reflex sym- pathetic dystrophy, and mechanical loosening. If motion gains are slow within the first 6 to 8 weeks, gentle manipulation under anesthesia may be beneficial. Delaying manipulation beyond 3 months after the scar has matured will increase the risk of periprosthetic fracture or tendon rupture. In these circumstances, arthrolysis, either arthroscopic or open, may be necessary. Arthro- scopic arthrolysis is particularly useful when there is limited scar formation, located primarily in the infrapatellar region, the intercondylar notch, and the peripatellar region. When the medial and lateral gutters are scarred, open arthrolysis is recommended. Management in the initial postoperative period after arthrolysis should include continuous epidural analgesia and supervised physical therapy. Occult sepsis may also predispose to stiffness after total knee arthroplasty. Diagnosing acute infection (within 4 weeks after surgery) is often difficult, as consti- Jess H. Lonner, MD, and Paul A. Lotke, MD Vol 7, No 5, September/October 1999 319 tutional symptoms, such as fevers and chills, are uncommon. The workup should include a complete blood cell count with differential, erythrocyte sedimentation rate, C- reactive protein assay, aspiration with culture and cell count, and plain radiographs. Nuclear medicine scans are difficult to interpret and lack accuracy in the early postoperative period. Occasionally, despite a thorough evaluation, no obvious cause of pain and motion loss is identified. Under these circumstances, continued ob- servation with time for resolution of the synovial inflammation may be indicated. Synovial biopsy with wound culture and frozen-section histoanalysis may be considered. 29 Mechanical factors may limit motion and cause pain. If a tight flexion gap is present, flexion will be limited. The femoral component may be oversized, tensing the retinaculum. This can often be treated by increasing slightly the posterior tibial slope or by recessing the posterior cruciate ligament in cruciate- retaining designs. A tight flexion space may also be present when the femoral component has a rotational imbalance, creating a trapezoidal flexion gap. This is addressed by recutting the femur and using a posterolateral wedge to ensure adequate external rotation of the femoral component. If a flexion contracture is being caused by a tight extension space, a posterior capsular release may be performed with assessment of residual posterior osteophytes, which would cause a relative contracture of the posterior capsule. This problem may also be addressed by resecting an additional portion of the distal femur. A posteriorly offset femoral component or an oversized femoral component may further decrease the flexion space. This can generally be addressed by downsizing the femoral component in a more appropriate position and resecting an additional portion of the posterior femoral condyle. Resecting additional tibia in this situation will be effective only if the extension space is com- parably tight. Otherwise, the flexion- extension mismatch will persist. In the presence of varus or valgus deformities, the medial capsular sleeve or lateral soft-tissue restraints must be balanced appropriately. Limited access to physical therapy or an inappropriate program may play a role in the development of stiffness. It appears that physical therapy, particularly in the initial period after total knee arthroplasty, is beneficial. With the current em- phasis on shorter hospitalization, it is critical that patients be enrolled expeditiously in supervised home physical therapy programs. It must be emphasized that lack of timely physical therapy or overzealous therapy may adversely affect motion. Poor patient motivation and low pain thresholds may also have a negative impact on motion gains. Potentially affected patients must be identified and coached through- out the postoperative period. Periprosthetic Femoral and Tibial Fractures Advanced osteoporosis, neurologic disorders, rheumatoid arthritis, chronic corticosteroid therapy, and notching of the anterior femoral cortex may predispose the patient to distal femur fracture after total knee arthroplasty. The relationship between femoral notching and subsequent fracture is often debated; however, in one study involving use of a biomechanical model, a 3- mm defect was shown to decrease the torsional strength of the distal femur by 29.2%. 30 Risk factors for periprosthetic tibial fractures are less well established, but are likely quite similar. Treatment depends on the fracture pattern, the medical and functional status of the patient, the integrity of the bone-prosthesis interfaces, and the quality of bone stock. Treatment options include immobilization in traction or a cast, open reduction and internal fixation, indirect reduction and fixation, and revision total knee arthroplasty. Orthogonal radiographs are critical to appropriately evalu- ate the fracture pattern. Traction views may be helpful. Nonoperative treatment is advisable for minimally displaced fractures when the alignment of the fracture and limb can be maintained in a well-molded long-leg or spica cast. In general, a cast can be used for 6 weeks, after which a switch to a long-leg hinged brace will allow early gentle range-of-motion exercises. The brace is worn until there is evidence of healing of the fracture as well as adequate quadriceps strength. Results of nonoperative treatment have been unsatisfactory, with high rates of motion loss, malalignment, nonunion, and systemic problems associated with prolonged immobilization. In the presence of malalignment, fracture displacement, or compromise of the prosthesis interfaces, surgical intervention is advisable. Open reduction and internal fixation may be performed with either intramedullary devices or a variety of plate constructs (Fig. 9). Inter- locked retrograde nailing may not be possible when certain posteriorly stabilized femoral components are used, when a closed box con- struct is present, or when there is inadequate distal bone stock. Ret- rograde nailing has the benefit of indirect reduction of the fracture without stripping the soft tissues. A large-diameter nail is preferred. Locking bolts may be applied to the distal interlocking screws to augment fixation when there is marked osteoporosis. An under- Aseptic Complications After Total Knee Arthroplasty Journal of the American Academy of Orthopaedic Surgeons 320

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