Injury, Int J Care Injured 48S5 (2017) S56–S60 Contents lists available at ScienceDirect Injury j o u r n a l h o m e p a g e : w w w e l s e v i e r c o m / l o c a t e / I n j u r y Anatomical and radiological evaluation of less invasive stabilisation system (LISS) in correlation with knee lateral collateral ligament insertion Florian Freimosera, Stephan Grecheniga, Anna Ofenhitzera, Bore Bakotab, Mario Staresinicc, Christian G Pfeifera,* a Department of Trauma and Orthopaedic Surgery, University Medical Centre Regensburg, Germany Trauma and Orthopaedic Surgery department, Brighton and Sussex University Hospital, NHS Trust, UK Trauma and Orthopaedic Clinic, University Hospital Merkur, Zagreb, Croatia b c K E Y W O R D S A B S T R A C T LISS Introduction: The Less Invasive Stabilisation System (LISS) is an angle-stable plate that enables treatment of distal femoral comminuted and periprosthetic fracture As it is placed through a minimally-invasive lateral approach, lateral knee pain is a commonly described symptom after its application This study investigates knee lateral collateral ligament (LCL) iatrogenic injury during LISS plate fixation A cadaver study was performed and a retrospective radiological investigation with the analysis of its clinical application was conducted to evaluate possible knee LCL damage Methods: The cadaver study included 13 human lower extremities, treated with LISS After application, lateral knee side was dissected, implants were removed and distances between the drill holes and LCL origin were measured In the retrospective radiological evaluation, postoperative X-rays for patients treated with distal femoral LISS plate in the University Hospital Regensburg, Germany from January 2010 to December 2015 were examined Following a protocol described by Pietrini et al., the LCL origin on postoperative X-rays was calculated, both in lateral and anterior-posterior (AP) view, and distances between the plate and its closest locking screw to the LCL origin were measured Results: In the cadaver study, the mean distance between the closest drilling hole and the ligament origin was 14.0 mm (range 9–21 mm; SD 3.8 mm) Twenty-two patients matched the inclusion criteria for the retrospective radiological study In lateral view, the mean distance between the origin and the closest locking screw was 6.3 mm (range 0–16.4 mm; SD 4.7 mm); the mean distance between the origin and the plate was 3.1 mm (range 0–13.9 mm; SD 4.1 mm) In AP view, the mean distance between LCL origin and the nearest screw was 2.4 mm (range 0–7.6 mm; SD 2.4 mm) The mean distance between the origin and the most distal locking screw was 9.2 mm (range 0–17.5 mm; SD 4.0 mm) Discussion: The LISS is a safe option to treat distal femoral fractures in respect to the LCL Due to close proximity, the LCL might be harmed; therefore, lateral knee pain or lateral instability after implantation should be assessed in further treatment distal femoral fracture periprosthetic fracture lateral collateral ligament outcome lateral knee pain femur © 2017 Elsevier Ltd All rights reserved Introduction The femoral Less Invasive Stabilisation System (LISS) was designed to address distal femoral fractures, mainly AO type A2-, A3-, C2- and C3.3 including periprosthetic fractures This system combines the advantages of a minimally-invasive osteosynthesis with an anglestable system Thus, distal femoral and femoral midshaft fractures, and * Corresponding author: Department of Trauma and Orthopaedic Surgery, University Medical Centre Regensburg, Franz-Josef-Strauss-Allee 11, 93053 Regensburg, Germany, phone: +49 941 944 6792, fax: +49 941 944 6806 E-mail: christian.pfeifer@ukr.de (C.G Pfeifer) 0020-1383 / © 2017 Elsevier Ltd All rights reserved comminuted and periprosthetic fractures can be treated with this system [1] In comminuted fractures, the plate is used as an internal fixator, which leaves the bone fragments within the comminuted zone untouched; the blood circulation related to these fragments is not further disturbed by the surgical procedure and osseous healing is facilitated [2] In periprosthetic fractures, the angle-stable plate design enables the surgeon to fix the plate without disturbing or damaging the femoral components of an existing knee arthroplasty Furthermore, minimally-invasive procedure enables soft tissue protection during osteosynthesis, which reduces the negative side effects of soft tissue trauma [3] Periprosthetic fractures after a total knee replacement (TKR) are particularly challenging to treat With the aging population, the F Freimoser et al / Injury, Int J Care Injured 48S5 (2017) S56–S60 number of comorbidities such as osteoporosis is growing Therefore, the incidence of total joint replacements is also increasing and is being followed by the numbers of periprosthetic fractures [4–6] Franklin et al described several risk factors for periprosthetic fractures: initial trauma, osteoporotic bones, aseptic loosening, revision arthroplasty, implant type and implantation technique, and the age of the patient were identified as independent risk factors for the occurrence of distal femoral periprosthetic fractures [6] Furthermore, comminuted fractures after a distal femoral highenergy trauma are life-changing events for patients [7] This is particularly the case when articulating surfaces like the femoral condyles or tibial plateau are involved Wasserstein et al reported that patients are 5.3-times more likely to undergo a total knee arthroplasty 10 years after tibial plateau fracture surgery compared with a matchedpopulation-based cohort [8] For both mentioned groups of patients, the LISS is a commonly used treatment option showing good results in short- and long-term followup [3,9] Weight et al showed that the LISS was a proper choice to stabilise mechanically-unstable, high-energy femoral fractures [10] It also enables early progression of weight-bearing, and early mobilisation of the knee joint Their patients showed no fixation failure, no varus collapse, and no cases of non-union However, lateral knee pain is a common and often described symptom after distal femur minimally-invasive plate osteosynthesis Symptoms range from pain upon movement to persistent pain during rest According to the literature, one of the adverse effects after LISS implantation is lateral knee pain that occurs as an irritation of the iliotibial tract [11–14] Further on, lateral collateral ligament (LCL) is at risk during LISS plate implantation due to its proximity to the LCL origin (Figures & 2a) [15] As the LISS is implanted through a small lateral approach without direct visualisation of the LCL, the question has emerged whether damage to the LCL during LISS implantation might also be a possible cause for lateral knee pain [14,16] The LCL of the knee is a round, string-shaped ligament that originates slightly posterior to the lateral femoral condyle midline Its S57 Fig A) Dissected right knee joint with implanted LISS Measured distances are green: LCL origin to most distal posterior drilling hole; blue: distance from anterior condyle edge to LCL origin; black: sagittal diameter lateral condyle B) Measurement on right dissected knee with marked screw holes and highlighted LCL distal insertion, together with femoral biceps muscle fibres, is located on the tip of the fibular head [17] The ligament is separated from the capsule of the knee joint with a thin fatty tissue layer Unlike the medial collateral ligament (MCL), it has no connection to the meniscus [18] MCL and LCL together are involved in knee flexion and extension and interact with the anterior and posterior cruciate ligaments (ACL and PCL) as central ligamentous structures [19] LCL also limits knee external rotation and serves as a varus stress protector [20] A cadaver study was conducted to evaluate the LISS plate distal tip proximity to LCL and the most distal posterior screw distance from the LCL origin and to investigate possible damage to the LCL during and after implantation of the LISS A retrospective radiological study of the patients who were treated in University Hospital in Regensburg was then performed to investigate the results of LISS clinical application Finally, the results of both studies were analysed for a correlation between the cadaver laboratory study and clinical LISS application Material and methods Cadaver study Fig Schematic of the anatomy of the knee joint relevant to the study In the cadaver study, 13 human cadavers embalmed with Thiel’s method were treated with the LISS (LISS Synthes-DePuy plate) [21] The entire minimally-invasive operative procedure was controlled by X-ray and was performed by a trained orthopaedic trauma physician, according to the specifications given by the manufacturer However, the treated femurs were uninjured at the time of the cadaver laboratory study Afterwards, the distal femur and proximal segment of the fibula were dissected and the implant was removed The three distal drilling S58 F Freimoser et al / Injury, Int J Care Injured 48S5 (2017) S56–S60 Fig Radiological measurement in lateral view A: Posterior edge of the femur axis; B: Perpendicular line through the most posterior point of Blumensaat’s line, C: Assumed origin of the LCL At the point of intersection of both lines (A and B) we orientated ourselves 0.4 mm dorsally and 11.7 mm distally (arrow) to encounter the origin of the LCL (C) holes were marked with pins (Figure 2b) The distance between the most distal posterior drilling hole and the macroscopic origin of the LCL was measured; this drill hole was the closest to the origin of the ligament in all cadavers Sagittal diameter of the lateral condyle and the distance between the frontal condyle edge and the origin were also measured to see if there was a correlation between the distance from the plate to the origin and the size of the distal femur Radiological outcome measurement All patients who underwent LISS distal femur osteosynthesis at University Hospital Regensburg between January 2010 and December 2015 were eligible for the study All patients treated for fracture fixation routinely undergo a postoperative X-ray check-up (one day, six weeks, six months and one year post-surgery) to check for malalignment, malposition, non-union or implant-related complications To detect the origin of the LCL on a conventional postoperative Xray, the method described by Pietrini et al was used [22] By using radiographic landmarks in both lateral and anterior-posterior (AP) projection, it is possible to calculate the origin of LCL The postoperative X-rays of all eligible patients were analysed and checked to see if these matched the criteria for LCL origin calculations X-ray inclusion and exclusion criteria To achieve reliable results, three radiographic landmarks need to be evaluated: 1) Blumensaat’s line, 2) the posterior edge of the femur in lateral projection, and 3) free sight on the most distal points of the femoral condyles X-rays that lacked direct sight to these radiographic landmarks were excluded from the study Further exclusion criteria were: an existing knee-prosthesis, because there is no radiographic sight on the relevant anatomical structures; highly dislocated fractures; injuries that were not compatible with an unharmed LCL; and X-rays showing an offset of the two condyles of more than 10 mm in lateral view Included X-rays (22 patients) were measured three times on three different dates, to avoid measuring errors Afterwards the mean value of the three measurements was calculated and used for further analysis To achieve real-life distances, we referred to the real-life diameter of the screw-holes (4.98 mm) in the LISS as given by the manufacturer, and cross-checked it with every single hole diameter in our Xrays to enable calculation of a correction factor All measurements were adjusted to the calculated correction factor by the following formula Fig Radiological measurement in anterior-posterior view: A: Condyle axis (line through the most distal points of both condyles); B: Perpendicular construction line on A, parallel to the lateral border of the lateral condyle; C Assumed origin of the LCL On the perpendicular construction line (B) there is a need to orientate 27.1 mm (double arrow) cranially to encounter the level of the origin of the LCL (C) F Freimoser et al / Injury, Int J Care Injured 48S5 (2017) S56–S60 Table Results of the radiological measurement in lateral view; distances given in mm Formula to calculate the real-life distance: real À life distance ¼ S59 4; 98 x measured distance measured hole diameter Lateral view [mm] Origin LCL – locking screw Origin LCL – Plate 6.3 16.4 0.0 4.7 3.1 13.9 0.0 4.1 Mean value Maximum Minimum SD X-ray analysis LATERAL In lateral projection, we marked a straight line on the posterior edge of the femoral axis and a perpendicular line to this axis, which runs through the most posterior point of Blumensaat’s line Corresponding to the findings of Pietrini et al., we used the point of intersection of both lines and orientated 0.4 mm dorsally and 11.7 mm distally The encountered point was the assumed centre of origin of the LCL (Figure 3) Afterwards, the shortest distance to the locking screws was measured To assume for deviations of the centre of the LCL, a 5-mmdiameter circle was drawn around the assumed centre of the origin All screws within this circle were assessed as an injury to the ligament Table Results of the radiological measurement in anterior-posterior view; distances given in mm AP view [mm] Mean value Maximum Minimum SD Origin LCL – closest screw Origin LCL – most distal screw 2.4 7.6 0.0 2.4 9.2 17.5 0.0 4.0 X-ray analysis ANTERIOR-POSTERIOR According to Pietrini et al., a line is drawn through the most distal points of both condyles of the femur (condyle axis) Afterwards, a perpendicular line to this condyle axis, parallel to the lateral border of the lateral condyle, is used On this perpendicular line, it is necessary to orientate 27.1 mm cranially to find the origin of the LCL (Figure 4) As all origins in the X-rays were concealed by the plate, or by a screw, we matched the corresponding X-ray in a lateral view, and measured the distance in AP view to the screw that was closest to the origin in lateral view Results Cadaver study In the cadaver study, the mean distance between the most distal posterior drilling hole and the origin of the ligament was 14.0 mm (range 9–21 mm; SD 3.8 mm) (Table 1) The mean sagittal diameter of the lateral femoral condyle was 71.8 mm (range 65–80 mm; SD 4.3 mm) The mean distance between the frontal condyle edge and the origin of the LCL was 45.8 mm (range 37–52 mm; SD 4.4 mm) There was no sign of injury in a predefined 5-mm safety buffer zone around the origin of the LCL Furthermore, there was no correlation between the size of the distal femur and the distance from the plate to the origin of the LCL destruction of the knee caused by the initial trauma was not compatible with an intact LCL Four of the 22 patients included in the radiological study had periprosthetic fractures Eight patients suffered a low-energy trauma, such as a simple fall Ten patients suffered a highenergy trauma, such as traffic accident or fall from a height The four remaining patients were treated with LISS because of a fracture treatment revision Of the 22 patients included in the radiological study, 12 were male and 10 were female, and the mean age of the 22 included patients was 52 years (SD 21 years) This radiological study showed a closer proximity between the origin of the LCL and the implant than did the anatomical study In lateral view, the mean distance between the origin and the closest locking screw was 6.3 mm (range 0–16.4 mm; SD 4.7 mm) (Table 2) The mean distance between the origin and the plate was 3.1 mm (range 0–13.9 mm SD 4.1mm) In nine patients, the plate and/or a locking screw were found within the pre-defined buffer zone (diameter mm) around the origin of the ligament In one case, the detected origin was directly in projection of the distal locking screw In AP projection, the mean distance between LCL origin and the nearest screw was 2.4 mm (range 0–7.6 mm; SD 2.4 mm) (Table 3) The mean distance between the origin and the most distal locking screw was 9.2 mm (range 0–17.5 mm; SD 4.0 mm) In one case, the detected origin was directly in the projection of a locking screw In two cases, the most distal locking screw was also the closest screw to the origin of the LCL Radiological outcome measurement There were 40 patients (22 female, 18 male) overall who underwent LISS distal femur osteosynthesis at our Level trauma centre between January 2010 and December 2015 The mean age of the patients was 61.2 years (SD 21 years) Twenty-two of the patients were included in our radiological study The remaining 18 patients did not match the inclusion criteria: 10 were excluded because of rotational misalignment of the X-ray; seven had no direct sight on the relevant anatomic structures due to a total knee arthroplasty; and for one patient, the Table Results of the cadaver study; distances given in mm [mm] Mean value Maximum Minimum SD Sagittal diameter Frontal condyloid edge – LCL LCL – most distal posterior screw 71.8 80.0 65.0 4.3 45.8 52.0 37.0 4.4 14.0 21.0 9.0 3.8 Discussion Distal femoral LISS is commonly used in surgical treatment of distal femur fractures Despite improvements in implant design and operation technique, some patients suffer from short- and long-term lateral knee pain after surgery [11] One possible cause is irritation of the iliotibial tract and disturbance of the LCL Therefore, this study was conducted to investigate in a cadaver study the proximity between the implant and the origin of the LCL In the cadaver study, there was no disturbance of the origin of the LCL as the mean distance between implant and origin was 14 mm Even the most proximal implant location showed a distance to the LCL origin of mm, thus not even touching the 5-mm buffer zone around the anatomical origin However, our cadaver study included only 13 cadavers and all femora were intact Furthermore, possible microscopic injuries cannot be ruled out, as there are no anatomical studies concerning the diameter of the origin of the ligament itself Also, the femoral LISS positioning in the cadaver laboratory was conducted under perfect conditions, with no bleeding and already reduced S60 F Freimoser et al / Injury, Int J Care Injured 48S5 (2017) S56–S60 (because unfractured) femora, which enables specific consideration of implant positioning To our knowledge no study investigating the distance between femur LISS implants and the LCL origin using human cadavers has been published so far; therefore, we cannot compare our results to those of other study groups In contrast, the radiological study showed a much closer relation of the plate position to the origin of the LCL The closer relation in our X-ray study may be caused by several reasons Firstly, all femora in the radiological study were fractured; therefore, shortening of the femur, malrotation and generally altered anatomical prerequisites are found during implant positioning Secondly, bleeding, soft tissue injuries and modified approaches (due to soft tissues) worsen the possibilities of correct implant positioning; thus, the relationship between the LCL origin and the plate might be closer Again – to our knowledge – no study has been conducted so far that evaluated LISS positioning on the femoral postoperative X-rays in relation to the LCL origin Liu et al reported an ideal implant position in 93% of the included cases (distal femur LISS and proximal tibia LISS) in a published case series [3] A meta-analysis that comprised 21 published papers of distal femoral fracture treatment using LISS included reports of only studies that evaluated the radiological malposition of the implant [1] Out of 694 treated fractures, 31 showed implant malpositioning, and this was considered to be a factor for postoperative and chronic pain [1] To which extent the involvement of the LCL origin contributes to the clinical symptoms after LISS plate malposition on a distal femur is not yet revealed and will have to be a subject of future studies Another contribution to closer proximity of the implant to the LCL origin in the clinical postoperative evaluation might be due to the calculation of the LCL origin using conventional X-rays The method used as described by Pietrini et al is an approximative method [22] However, a more precise method for postoperative evaluation of the position of the implanted LISS to the LCL origin will require computed tomography, which is not routinely applied after fracture fixation in this anatomical region As identified in the cadaver study, the most distal posterior drilling hole was the closest hole to the origin of the LCL; whereas in the radiological study, the most distal hole was the closest hole in 10 out of 22 patients This might be an additional cause for differing results between cadaver and clinical study and mirrors differences in implant positioning between a cadaver laboratory setting and intraoperative positioning as discussed above Both parts of the presented investigation can only be seen as case series Further studies will implement prospective evaluation of lateral knee stability and lateral knee pain upon knee varus stress after LISS osteosynthesis Together with X-ray findings this will provide a better understanding whether the effect on the LCL origin is responsible for lateral knee pain after LISS application on the distal femur Nevertheless, it will be still difficult to distinguish between LCL and iliotibial tract as a cause of postoperative lateral knee pain Taken together, we concur with other publications that the LISS is a proper and safe way to treat distal femur fractures [10,14,23] The origin of the LCL is close to the implant, and as a result, may be harmed by the locking screws of the plate If a patient suffers from lateral knee pain or lateral knee instability after LISS implantation, the surgeon should consider LCL injury as a potential cause To prevent secondary knee osteoarthritis, a careful physical examination of the knee joint with respect to lateral knee instability should be conducted In cases where implant removal is indicated with the simultaneous presence of lateral knee instability, we recommend a wider lateral approach to the knee to visualise the LCL origin and to be able to reconstruct the LCL when needed Conflict of interest The authors are not compensated and there are no other institutional subsidies, corporate affiliations, or funding sources supporting this work unless clearly documented and disclosed References [1] Smith TO, Hedges C, MacNair R, Schankat K, Wimhurst JA The clinical and radiological outcomes of the LISS plate for distal femoral fractures: a systematic review Injury 2009;40:1049–63 [2] Perren SM Evolution of the internal fixation of long bone fractures The scientific basis of biologicalinternal fixation: choosing a new balance between stability and biology J Bone Joint Surg Br 2002;84:1093–110 [3] Liu F, Tao R, Cao Y, Wang Y, Zhou Z, Wang H et al The role of LISS (less invasive stabilisation system) in the treatment of peri-knee fractures Injury 2009;40:1187–94 [4] Frenzel S, Vécsei V, Negrin L Periprosthetic femoral fractures—incidence, classification problems and the proposal of a modified classification scheme Int Orthop 2015;39:1909–20 [5] Ruchholtz S, Tomás J, Gebhard F, Larsen MS Periprosthetic fractures around the knee—the best way of treatment Eur Orthop Traumatol 2013;4:93–102 [6] Franklin J, Malchau H Risk factors for periprosthetic femoral fracture Injury 2007;38:655–60 [7] Sanders DW, MacLeod M, Charyk-Stewart T, Lydestad J, Domonkos A, Tieszer C Functional outcome and persistent disability after isolated fracture of the femur Can J Surg 2008;51:366–70 [8] Wasserstein D, Henry P, Paterson JM, Kreder HJ, Jenkinson R Risk of total knee arthroplasty after operatively treated tibial plateau fracture: a matched-population-based cohort study J Bone Joint Surg Am 2014;96:144–50 [9] Ricci WM, Loftus T, Cox C, Borrelli J Locked plates combined with minimally invasive insertion technique for the treatment of periprosthetic supracondylar femur fractures above a total knee arthroplasty J Orthop Trauma 2006;20:190–6 [10] Weight M, Collinge C Early results of the less invasive stabilization system for mechanically unstable fractures of the distal femur (AO/OTA types A2, A3, C2, and C3) J Orthop Trauma 2004;18:503–8 [11] Fankhauser F, Gruber G, Schippinger G, Boldin C, Hofer HP, Grechenig W et al Minimalinvasive treatment of distal femoral fractures with the LISS (Less Invasive Stabilization System): a prospective study of 30 fractures with a follow up of 20 months Acta Orthop Scand 2004;75:56–60 [12] Babst R, Bavonratanavech S, Pesantez R Minimally Invasive Plate Osteosynthesis (MIPO) Stuttgart: Georg Thieme Verlag; 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