Chronic extensor mechanism insufficiency around TKA is a very challenging pathology to treat. An insufficient extensor mechanism negatively affects implant survival and patient outcomes. There are several risk factors for extensor mechanism disruption and the surgeon should be aware and avoid these problems in the perioperative period. In appropriately selected patients, reconstruction of the extensor mechanism is a valid option. Whole extensor mechanism and Achilles tendon allograft reconstruction of the deficient extensor mechanism have been proposed with good early published results. These reconstructions, however, are expensive and with time may stretch and lead to recurrence of an extensor lag. An alternative to allograft, is the use of Marlex mesh as popularised by Browne and Hanssen. This technique uses a knitted monofilament polypropylene mesh that is secured to the patient's native lateral tissue and covered by an appropriately dissected and distalised vastus medialis muscle. The technique can be used for both patellar and quadriceps tendon deficiencies and can be done with or without implant revision and is currently the treatment of choice at the presenter's institution. The surgeon should be aware of the complexity and limitations of these three reconstructive techniques

A key component to the success of total knee replacement is the health and integrity of the extensor mechanism. While there are issues related to the patella, such as fracture, dislocation, subluxation, clunk due to peripatellar fibrosis and anterior knee pain, the overall integrity of the extensor mechanism is of tantamount importance in providing an excellent functional outcome. During total knee replacement it is of utmost importance to preserve the anatomic insertion of the patellar tendon on the tibial tubercle. However, after total knee replacement, a fall or extreme osteoporosis of the patella may cause a rupture of the patellar tendon, distally or proximally, and possibly the quadriceps tendon off of the proximal pole of the patella. Simple repairs of the patellar tendon avulsion may involve use of the semitendonosis and gracilis tendons along with primary repair of the tendon. Usually, patella infera develops after such a repair affecting overall strength and function. For severe disruptions of the extensor mechanism that are accompanied by a significant extensor lag, autologous tissue repair may not be possible. Thus, there are three techniques for reconstruction of this difficult problem: Extensor mechanism allograft with bone-patellar tendon-patella-quadriceps tendon, extensor mechanism allograft with os calcis-Achilles tendon construct and Marlex-mesh reconstruction for patellar tendon avulsion. The key to success of extensor mechanism allograft is proper tensioning of the allograft at full extensor and immobilisation for 6 weeks. Rosenberg's early experience showed that the allograft works best placed at maximum tension in extension. Rubash has described the use of the os calcis-Achilles tendon which does not utilise a patellar substitute. Hansen has recently described excellent results with the use of Marlex mesh to act as a structural reinforcement to the patellar tendon when it is avulsed

Extensor mechanism complications after or during total knee arthroplasty are problematic. The prevalence ranges from 1–12% in TKR patients. Treatment results for these problems are inferior to the results of similar problems in non-TKR patients. Furthermore, the treatment algorithm is fundamentally different from that of non-TKR patients. The surgeon's first question does not focus on primary fixation; rather the surgeon must ask if the patient needs surgery and if so am I prepared to augment the repair? Quadriceps tendon rupture, periprosthetic patellar fracture, and patellar tendon rupture have similar treatment algorithms. Patients who are able to perform a straight leg raise and have less than a 20-degree extensor lag are generally treated non-operatively with extension bracing. The remaining patients will need surgical reconstruction of the extensor mechanism. Loose patellar components are removed. Primary repair alone is associated with poor results. Whole extensor mechanism allograft, Achilles tendon allograft, and synthetic mesh reconstruction are the current techniques for augmentation. In the acute setting if these are not available hamstring tendon harvest and augmentation is an option. Achilles tendons and synthetic mesh are easier to obtain than and entire extensor mechanism but are limited to patients that have an intact patella and the patella that can be mobilised to within 2–3 cm of the joint line. No matter which technique is used the principles are: rigid distal/tubercle fixation, coverage of allograft/mesh with host tissue to decrease infection, tensioning the augment material in extension, no flexion testing of reconstruction and post-operative extension bracing

A key component to the success of total knee replacement is the health and integrity of the extensor mechanism. While there are issues related to the patella, such as fracture, dislocation, subluxation, clunk due to peripatellar fibrosis and anterior knee pain, the overall integrity of the extensor mechanism is of tantamount importance in providing an excellent functional outcome. During total knee replacement it is of utmost importance to preserve the anatomic insertion of the patellar tendon on the tibial tubercle. However, after total knee replacement, a fall or extreme osteoporosis of the patella may cause a rupture of the patellar tendon, distally or proximally, and possibly the quadriceps tendon off of the proximal pole of the patella. Simple repairs of the patellar tendon avulsion may involve use of the semitendonosis and gracilis tendons along with primary repair of the tendon. Usually, patella infera develops after such a repair affecting overall strength and function. For severe disruptions of the extensor mechanism that are accompanied by a significant extensor lag, autologous tissue repair may not be possible. Thus, there are three techniques for reconstruction of this difficult problem: Extensor mechanism allograft with bone-patellar tendon-patella-quadriceps tendon, extensor mechanism allograft with os calcis-Achilles tendon construct and Marlex-mesh reconstruction for patellar tendon avulsion. The key to success of extensor mechanism allograft is proper tensioning of the allograft at full extensor and immobilisation for 6 weeks. Rosenberg's early experience showed that the allograft works best placed at maximum tension in extension. Rubash has described the use of the os calsis-Achilles tendon which does not utilise a patellar substitute. Hansen has recently described excellent results with the use of Marlex mesh to act as a structural reinforcement to the patellar tendon when it is avulsed

Extensor mechanism complications after or during total knee arthroplasty (TKA) are problematic. The prevalence ranges from 1%-12% in TKA patients. Treatment results for these problems are inferior to the results of similar problems in non-TKA patients. Furthermore, the treatment algorithm is fundamentally different from that of non-TKA patients. The surgeon's first question does not focus on primary fixation; rather the surgeon must ask if the patient needs surgery and if so am I prepared to augment the repair? Quadriceps tendon rupture, peri-prosthetic patellar fracture, and patellar tendon rupture have similar treatment algorithms. Patients who are able to perform a straight leg raise and have less than a 20-degree extensor lag are generally treated non-operatively with extension bracing. The remaining patients will need surgical reconstruction of the extensor mechanism. Loose patellar components are removed. Primary repair alone is associated with poor results. Whole extensor mechanism allograft, Achilles tendon allograft, and synthetic mesh reconstruction are the current techniques for augmentation. In the acute setting if these are not available, hamstring tendon harvest and augmentation is an option. Achilles tendons and synthetic mesh are easier to obtain than an entire extensor mechanism but are limited to patients that have an intact patella and the patella that can be mobilised to within 2–3 cm of the joint line. No matter which technique is used the principles are: rigid distal/tubercle fixation, coverage of allograft/mesh with host tissue to decrease infection, tensioning the augment material in extension, no flexion testing of reconstruction and post-operative extension bracing

Introduction: knee revision in absence of Extensor Mechanism has been always a challenging problem in Orthopaedics. Many authors are in favour to abandone any endoprosthetic substitution in front of such a situation. We think osteotendinous allografts, in this particular case whole Extensor Mechanism allografts, could play an essential role before any Knee Arthrodesis. Material and Method: From 1999 up to 2004 11 patients (4 male, 7 female) (mean age 72, range 68 to 86) underwent to a whole Extensor Mechanism allografting procedure. Mean follow up was 2.7 years (1 to 5 years). In the first four cases a whole Extensor Mechanism allograft was implanted, while the next seven cases the allograft was reinforced by means of a Leeds-Keio Dacron band. Results: There was no infections in this serie. The mean obtained R.O.M. in the first three months was – 5 of active extension (range 0 to −15) and 95 active flexion (range 80 – 110). However 3 from the 4 former operated cases had a progressive loss of active extension up to −25 (range −20 to −35) at 18 months, that did not increase after this period. Ultrasonic exams showed a lengthening of the patellar tendon in these cases. None of these 3 patients wished to undergo to a patellar tendon reinforcement. On the other hand those later cases, where patellar tendon was reinforced did not show any change over the time (at 18 months mean active extension was maintained to −5 (range 0 to 15). Conclusions: Extensor mechanism allografts are very useful in difficult knee revisions with absence of extensor mechanism, so that knee arthrodesis is not the method of choice for these patients. However augmentation of patellar tendon is necessary to maintain with the years an active extension

Disruption of the extensor mechanism in total knee arthroplasty may occur by tubercle avulsion, patellar or quadriceps tendon rupture, or patella fracture, and whether occurring intra-operatively or post-operatively can be difficult to manage and is associated with a significant rate of failure and associated complications. This surgery is frequently performed in compromised tissues, and repairs must frequently be protected with cerclage wiring and/or augmentation with local tendon (semi-tendinosis, gracilis) which may also be used to treat soft-tissue loss in the face of chronic disruption. Quadriceps rupture may be treated with conservative therapy if the patient retains active extension. Component loosening or loss of active extension of 20° or greater are clear indications for surgical treatment of patellar fracture. Acute patellar tendon disruption may be treated by primary repair. Chronic extensor failure is often complicated by tissue loss and retraction can be treated with medial gastrocnemius flaps, achilles tendon allografts, and complete extensor mechanism allografts. Attention to fixing the graft in full extension is mandatory to prevent severe extensor lag as the graft stretches out over time

Extensor mechanism disruption in total knee arthroplasty (TKA) occurs infrequently but often requires surgical intervention. We compared two cohorts undergoing extensor mechanism allograft reconstruction, one group had an extensor mechanism rupture, and the other had a recurrent ankylosed knee. Thirteen consecutive patients with extensor mechanism disruption or ankylosis after TKA were treated. Two different types of extensor mechanism allografts were used: quadriceps tendon-patella-patella tendon-tibial tubercle, and Achilles tendon allograft(Fig1). Demographic factors, diagnosis at extensor failure, Knee Society clinical rating scores, radiographs, and patient satisfaction were recorded. The average time from extensor mechanism disruption to surgery was 6.6 months (range, 1-24 months). At a mean followup of 24 months (range, 6-46 months), all patients were community ambulators. None of the patients showed a postoperative extensor lag. Average postoperative maximum flexion was 97° (90-115°) for the ruptured group and 80° (75-90) for the ankylosed grup. All patients thought their functional status had improved, and 87% were satisfied with the results of the allograft reconstruction (Fig 2, 3, 4, 5). One patient had allograft failure due to recurrent infection after re-revision for sepsis. The total extensor mechanism allograft and Achilles tendon allograft both were successful in the treatment of the failed extensor mechanism and showed promising results for the treatment of the ankylosed knee

Anterior knee pain attributable to the patellofemoral joint and extensor mechanism dysplasia is a common presentation to Orthopaedic surgeons. Plain radiology is likely to remain the primary investigation of the knee in most centres, but most of the radiological features of extensor mechanism dysplasia are time consuming and difficult to measure reproducibly. 137 consecutive symptomatic knees aged under 30, referred to an Orthopaedic surgeon were studied in order to identify a rapid and reproducible marker for those knees worthy of further in-depth analysis. Overall, 67 knees (49%) had at least one radiological abnormality and 70 (51%) were considered ‘normal’. There were 5 Dejour Type3 dysplasias of the femoral trochlea, 9 Type2 and 12 Type1. There were 49 cases of patella alta and 5 of patella infera. Four knees had an abnormal lateral patellofemoral (patellar tilt) angle. 15 knees had more than one abnormality. The classification of trochlear dysplasia was difficult and showed poor reproducibility. This was also true for the measurement of lateral patellofemoral angles. Patellar height was more easily measured but took time. The sulcus angle emerged as an easily and rapidly measurable feature that was reproducible and was closely related to the other features of extensor mechanism dysplasia. The sulcus angle offers a rapid and reliable ‘screening’ measurement on knee radiographs. A normal sulcus angle suggests that seeking the other radiological markers of extensor mechanism malalignment is unlikely to reveal additional useful information. Other diagnoses can then be sought. The more abnormal the sulcus angle, the more severe the other features of extensor mechanism dysplasia are likely to be. Further detailed measurements can then help to define the most appropriate surgical correction

We describe the influence of the angle of immobilisation during partial weight-bearing on the forces across the extensor mechanism of the knee. Gait analysis was performed on eight healthy male subjects with the right knee in an orthotic brace locked at 0°, 10°, 20° and 30°, with the brace unlocked and also without a brace. The ground reaction force, the angle of the knee and the net external flexion movement about the knee were measured and the extensor mechanism force was calculated. The results showed a direct non-linear relationship between the angle of knee flexion and the extensor mechanism force. When a brace was applied, the lowest forces occurred when the brace was locked at 0°. At 30° the forces approached the failure strength of some fixation devices. We recommend that for potentially unstable injuries of the extensor mechanism, when mobilising with partial weight-bearing, the knee should be flexed at no more than 10°

Anterior knee pain due to dysplasia of the extensor mechanism is common. We have studied 137 knees (103 patients) in order to identify a rapid and reproducible radiological feature which would indicate the need for further analysis. Overall, 67 knees (49%) had at least one radiological abnormality; 70 (51%) were considered normal. There were five cases of Dejour type-3 dysplasia of the femoral trochlea, nine of type-2 and 12 of type-1. There were 49 cases of patella alta and five of patella infera. Four knees had an abnormal lateral patellofemoral angle (patellar tilt), and in 15 knees there was more than one abnormality. Classification of trochlear dysplasia was difficult and showed poor reproducibility. This was also true for the measurement of the lateral patellofemoral angle. Patellar height was more easily measured but took time. The sulcus angle is an easily and rapidly measurable feature which was reproducible and was closely related to other features of dysplasia of the extensor mechanism. The finding of a normal sulcus angle suggested that seeking other radiological evidence of malalignment of the extensor mechanism was unlikely to reveal additional useful information. The severity of other features of dysplasia of the extensor mechanism correlated with increasing sulcus angle

High-energy injuries involving the proximal tibia sometimes result in significant soft tissue injuries that may create an incompetent knee extensor mechanism. Reconstruction of the extensor mechanism using the gastrocnemii has been previously described in those patients with tissue loss following either arthroplasty or tumour surgery. In 2009, a single cross-sectional study of eight patients described the technique after trauma, and their outcome at an average of 24 months. Use of a gastrocnemius rotational myoplasty has been described in the literature for six additional cases following trauma. We present our indications, technique and 5-year results of a separate series of four patients in whom the extensor mechanism of the knee was rendered incompetent after direct tissue loss, or subsequent infection, secondary to trauma. In each case, after stabilisation of the periarticular fracture and control of infection, the medial gastrocnemius was employed both to reconstruct the patellar ligament, and to simultaneously restore soft tissue coverage. Three out of 4 patients had excellent outcomes, have returned to their previous occupations and participate in regular sport. The overall mean scores were: Oxford knee Score (38.25), Knee Injury and Osteoarthritis Outcome Score (KOOS) (64.5) and Modified Cincinnati Score (68.25). Mean knee ROM was 5–97 degrees. Video for basic gait analysis was recorded. For those traumatic injuries with the difficult combination of a soft tissue deficit and incompetence of the knee extensor mechanism, we believe the medial gastrocnemius rotational myoplasty provides an excellent reconstructive option to address both of these fundamental problems simultaneously

General Principles. All repairs should be repaired in full extension. Repairs should be immobilised in full extension for 6–12 weeks. Gradual resumption of motion in a hinged brace over an additional 6–8 weeks almost always yields flexion to at least 90 degrees. Marlex mesh has been shown to be an excellent replacement as well as an augment for deficient soft tissue. Acute tibial tuberosity avulsion. Open repair is best accomplished with a non-absorbable heavy Krackow suture, secured distally around a screw and washer followed by 6 to 8 weeks of immobilization. Augmentation with a semitendinosus graft or Marlex mesh can provide additional support. Acute Patella Tendon Rupture. End-to-end repair is standard, but re-rupture is not uncommon, so supplemental semitendinosus reconstruction is recommended. The tendon is harvested proximally, left attached distally and passed through a transverse hole in the inferior patella. The gracilis tendon can be harvested and sutured to semitendinosus for additional length, if needed. Acute Quadriceps Tendon Rupture. These can be repaired end-to-end with a non-absorbable heavy Krackow suture. A superficial quadriceps fascial turndown or mesh may be a useful adjunct. Patella Fracture. Treatment depends on the status of the patellar component and the loss of active extension. If the component remains well fixed and the patient has less than a 20-degree lag, non-operative treatment in extension. A loose component and/or > 20-degree extensor lag requires ORIF +/− component revision. Chronic Disruptions. While standard repair techniques are possible, tissue retraction usually prevents a “tension-free” repair. If the patella remains viable and has not retracted proximally an Achilles tendon graft is appropriate. In chronic disruptions with loss of the patella, allograft extensor mechanism reconstruction may be considered. Marlex mesh repair has also been shown to be effective in reconstruction of chronic patellar and quadriceps tendon defects

In patients with significant bone loss and a nonfunctioning extensor mechanism, the approach to revision is complicated. We describe a unique approach to solve this complex problem to help restore clinically satisfactory results. Our technique involves the use of a donor allograft that consists of proximal tibia along with the attached extensor mechanism (patellar tendon-patella-quadriceps tendon). Five reconstructions utilizing bone allografts and extensor mechanisms were performed by two surgeons. Each has extensive surgical history on the affected knee and presented with gross instability, considerable bone loss, and significant extensor lag or total loss of extension. The implants used were press-fit stems with the tibial baseplate cemented into the allograft prior to implantation. In this series, either hinged or total stabilized prostheses were used. The follow up ranged from 1 to 5 years. The only complication to date was reported in one patient who required irrigation and debridement with surgical wound closure after partial dehiscence. However the patency of the allograft was not disrupted. All prostheses have been noted to be stable with no signs of loosening. This procedure presented should be considered a salvage procedure for bone stock and extensor mechanism deficiency in revision total knee arthroplasty. The advantage to our allograft is the inherent stability of the proximal tibia with the tibial tubercle and associated extensor mechanism. For patients with this complex deficiency, there has been no effective method of treatment and we advocate the use of this procedure to restore function and relieve pain to an otherwise grossly unstable and functionally limited joint

Objective:. Accurate measurement of the extension and flexion gap is important in total knee arthroplasty (TKA). Particularly, the flexion gap may be influenced by several factors; therefore, tension of the posterior cruciate ligament (PCL), knee extensor mechanism, and the thigh weight may need to be considered while estimating the flexion gap. However, there is no comprehensive study on the flexion gap, including an assessment of the influence of gravity on the gap. The purpose of this study is to investigate the influence of PCL, knee extensor mechanism, and thigh weight on the flexion gap by using a fresh frozen cadaver. Methods:. A fresh frozen lower limb that included the pelvis was used for the assessments. The knee was resected by a measured resection technique and a femoral component was implanted to estimate the component gap. The knee was flexed by precisely 90 degrees using a computer navigation system. The flexion gap was measured in different situations: group A, PCL preserved and patella reduced; group B, PCL preserved and patella everted; group C, PCL resected and patella reduced; and group D, PCL resected and patella everted. In each group, the measurements were obtained under 3 different conditions: 1, knee flexed and the lower limb on the operation table under gravity, as is usually done in TKA; 2, hip and knee flexed 90 degrees to avoid the influence of gravity; and 3, knee set in the same position as in condition 1 and the thigh was held by hand to reduce the influence of the thigh weight. Results:. The flexion gap differed according to groups and conditions. Group B was larger than group A in most conditions and group D was larger than group C. The flexion gap in group D was the largest among the 4 groups. The extensor mechanism had influences to the flexion gap (Table 1). In groups A and B, the flexion gaps were similar under conditions 1, 2, and 3; however, in groups C and D, the flexion gaps in condition 1 were smaller than those in conditions 2 and 3. The thigh weight condition had influences to the flexion gap when the PCL was resected (Table 2). Conclusion:. This is the first systemic report about the influences of PCL, extensor mechanism, and thigh weight on flexion gap measurement in TKA. PCL, extensor mechanism, and thigh weight influence the flexion gap and should be considered during TKA surgery. Especially, careful consideration is necessary to estimate the flexion gap when the PCL is resected and the patella is everted because the flexion gap becomes much wider than other situations

Complications involving the knee extensor mechanism occur in 1% to 12% of patients following total knee arthroplasty (TKA), and have negative effects on patient outcomes. While multiple reconstruction options have been described for complete disruption of the extensor mechanism, the results in patients with a prior TKA are inferior to those in patients without a TKA, and frequently have required the use of allograft tendon grafts which can attenuate and stretch over time. However, encouraging results have been reported by Browne and Hanssen in treatment of patellar tendon disruption with the use of a synthetic mesh (knitted monofilament polypropylene). In this technique, a synthetic graft is created by folding a 10 × 14 inch sheet of mesh and securing it with non-absorbable sutures. A burr is then used to create a trough in the anterior aspect of the tibia to accept the mesh graft. The graft is inserted into the trough and secured with cement. After the cement cures, a transfixion screw with a washer is placed. A portal is subsequently created in the soft tissues lateral patellar tendon remnants to allow delivery of the graft from deep to superficial. The patella and quadriceps tendon are mobilised, and the graft is secured with sutures to the lateral retinaculum, vastus lateralis, and quadriceps tendon. The vastus medialis is then mobilised and brought in a pants-over-vest manner over the mesh graft, and secured with additional sutures. Finally, the distal arthrotomy is closed tightly to completely cover the mesh graft with host tissue. In their series, Browne and Hanssen noted that 9 of 13 patients achieved an extensor lag of <10 degrees with preserved knee flexion and significant improvements in the mean Knee Society scores for pain and function. A similar modified method has been used at our institution for chronic quadriceps tendon disruptions as well. The reconstructions have shown less of a tendency to late attenuation, stretch and recurrent extensor lag beyond two years compared to our experience with tendon allograft reconstructions and remains our procedure of choice at our institution for the majority of these challenging problems

Purpose: This study was carried out in order to assess the results of reconstruction of a deficient extensor mechanism in the presence of total knee replacement using Connective Tissue Prosthesis (CTP). Methods & results: The CTPs are available as flat tapes constructed from polyester in an open weave structure. They were used to reinforce and reconstruct the extensor mechanism which was deficient in three patients who had undergone total knee replacement or were about to undergo total knee replacement. Two cases had extensor mechanism deficiency as a complication following total knee replacement while the third case had extensor mechanism deficiency at the time of the primary knee reconstruction. The average follow-up was one year. All three cases showed good results with no extension lag and good range of movement at follow up. Conclusion: A Connective Tissue Prosthesis Reconstruction of the knee extensor mechanism offers a good option for the management of the uncommon but difficult problem of extensor mechanism deficiency in patients with a total knee arthroplasty

General Principles: All repairs should be repaired in full extension. Repairs should be immobilised in full extension for 6–12 weeks. Gradual resumption of motion in a hinged brace over an additional 6–8 weeks almost always yields flexion to at least 90 degrees. Marlex Mesh has been shown to be an excellent replacement as well as an augment for deficient soft tissue. Acute tibial tuberosity avulsion: Open repair is best accomplished with a non-absorbable heavy Krackow suture, secured distally around a screw and washer followed by 6 to 8 weeks of immobilization. Augmentation with a semitendinosus graft or Marlex can provide additional support. Acute Patella Tendon Rupture: End-to-end repair is standard, but re-rupture is not uncommon, so supplemental semitendinosus reconstruction is recommended. The tendon is harvested proximally, left attached distally and passed through a transverse hole in the inferior patella. The gracilis tendon can be harvested and sutured to semitendinosus for additional length, if needed. Acute Quadriceps Tendon Rupture: These can be repaired end-to-end with a non-absorbable heavy Krackow suture. A superficial quadriceps fascial turndown or mesh may be a useful adjunct. Patella Fracture: Treatment depends on the status of the patellar component and the loss of active extension. If the component remains well fixed and the patient has less than a 20-degree lag, non-operative treatment in extension. A loose component and/or > 20-degree extensor lag requires ORIF +/− component revision. Chronic Disruptions: While standard repair techniques are possible, tissue retraction usually prevents a “tension-free” repair. If the patella remains viable and has not retracted proximally an Achilles tendon graft is appropriate. In chronic disruptions with loss of the patella, allograft extensor mechanism reconstruction may be considered. Marlex mesh repair has also been shown to be effective in reconstruction of chronic patellar and quadriceps tendon defects

Patella and extensor mechanism injuries are common injuries and are generally managed with some degree of immobilisation and partial weight bearing to facilitate healing. The aim of this project was to determine the type of immobilisation or splintage during partial weight bearing that results in minimal forces acting through the extensor mechanism. Gait analysis studies were performed on eight healthy male subjects mobilising partially weight bearing. Measurements were taken for six types of immobilisation: locked at 0, 10, 20, 30 degrees and unlocked in an orthotic knee brace, and without a brace. The ground reaction force, knee joint angle and the knee flexion moment were measured using Qualisys Track Manager and Visual 3D Software. The extensor mechanism moment and the extensor mechanism force were calculated using static equilibrium equations and documented data. A one-way analysis of variance statistical test was performed to determine the statistical significance of the differences between the six types of immobilisation. There was a direct relationship between the knee flex-ion angle and the extensor mechanism force. The extensor mechanism force at 0 degrees of immobilisation was significantly lower than that for 20 and 30 degrees (p< 0.05). The increase in the extensor mechanism moment arm with increasing knee flexion was not suf-ficient to offset the increase in the extensor mechanism force caused by the increase in the knee flexion moment. The results also showed that the knee flexion angle does not always correspond with the angle set at the knee brace; however they did exhibit a direct relationship. These results have important implications for the management of patients with patella and extensor mechanism injuries. The results suggest that improvements in knee brace design to allow 0 degrees of knee flexion, rather than the 10 degrees as seen in this study, are likely to result in significantly reduced extensor mechanism tensile forces

General Principles - All repairs should be repaired in full extension. Repairs should be immobilised in full extension for 6–12 weeks. Gradual resumption of motion in a hinged brace over an additional 6–8 weeks almost always yields flexion to at least 90 degrees. Marlex Mesh has been shown to be an excellent replacement as well as an augment for deficient soft tissue. Acute Tibial Tuberosity Avulsion - Open repair is best accomplished with a non-absorbable heavy Krackow suture, secured distally around a screw and washer followed by 6 to 8 weeks of immobilisation. Augmentation with a semitendinosus graft or Marlex can provide additional support. Acute Patella Tendon Rupture - End-to-end repair is standard, but re-rupture is not uncommon, so supplemental semitendinosus reconstruction is recommended. The tendon is harvested proximally, left attached distally and passed through a transverse hole in the inferior patella. The gracilis tendon can be harvested and sutured to semitendinosus for additional length, if needed. Acute Quadriceps Tendon Rupture - These can be repaired end to end with a non-absorbable heavy Krackow suture. A superficial quadriceps fascial turndown or mesh may be a useful adjunct. Patella Fracture - Treatment depends on the status of the patellar component and the loss of active extension. If the component remains well fixed and the patient has less than a 20-degree lag. A loose component and/or >20-degree extensor lag requires ORIF +/− component revision. Chronic Disruptions - While standard repair techniques are possible, tissue retraction usually prevent a “tension-free” repair. If the patella remains viable and has not retracted proximally an Achilles tendon graft is appropriate while in any patellar tendon defect, mesh repair has been shown to be effective. In most chronic disruptions with loss of the patella allograft extensor mechanism reconstruction may be considered