Popliteus tendon impingement after correct-sized total knee arthroplasty, a case report

C.R. Quispel1,2 S.R. Beekhuizen2 M.M. Bruin2 R. de Ridder1 1 Department of Orthopaedic Surgery, Langeland Ziekenhuis, Zoetermeer, the Netherlands 2 Department of Orthopaedic Surgery, HagaZiekenhuis, the Hague, the Netherlands

Popliteus tendon impingement after total knee arthroplasty is a complication that is not frequently diagnosed in correct-sized total knee arthroplasty. Popliteus tendon impingement can be diagnosed by ultrasound guided analgesic injections and is mostly managed by conservative treatment. However, in this case report we describe a 62-year-old female with posterolateral knee pain after a total knee arthroplasty which was treated surgically. Postoperative X-rays did not show any sign of complications. X-rays also confirmed that no under- or oversized prosthetic components were used. The total knee prosthesis showed a good functional outcome, but ultrasound imaging showed tendinopathy of the popliteus tendon . Initial treatment consisted of ultrasound guided injections in the popliteus tendon region. Eventually, the popliteus tendon had to be released surgically to obtain a long-term satisfactory result. Popliteus tendon impingement after total knee arthroplasty should be considered as a possible cause for posterolateral pain after total knee arthroplasty. Surgical treatment could be considered when conservative treatment fails to provide lasting satisfactory results.

Introduction Total knee arthroplasty (TKA) is one of the most effective treatment options for end-stage knee osteoarthritis to improve function and reduce pain.1 Residual pain after joint replacement is a common complication after TKA.2 A rare cause for residual pain is popliteus tendon impingement (PTI). During surgery, it is advised to protect the popliteus tendon (PT) while performing TKA, as it is prone to iatrogenic injury. Its transection can affect flexion gap balancing.3,4 A recent study showed that PTI could play a role in residual pain and stiffness after TKA.5 Diagnostic ultrasound-guided injections with anesthetics may confirm PTI and can, in combination with local corticosteroids, provide symptomatic pain relief in some patients.6 To our knowledge, there are only a few studies available regarding post-operative anatomical impingement and most of them are cadaveric studies. In addition, there is no recent literature available concerning arthroscopic versus open surgical treatment when conservative treatment fails.6-8 We report a case where PTI after TKA is identified as cause for residual posterolateral knee pain, treated with a lateral mini arthrotomy to release the popliteus tendon (PT) and scar tissue.

Patient A 62 year old woman visited the outpatient clinic in 2013. Her X-ray showed a Kellgren and Lawrence (K&L) classification grade 4 osteoarthritis of the left knee. Her medical history of the left knee consisted of an open medial meniscectomy and arthroscopic partial lateral meniscectomy. Previously, varicose surgery was done in the back of the left knee. Conservative treatment through several intra-articular injections with bupivacaine/triamcinolone was started in 2010, but appeared no longer a sufficient treatment option. A Cruciate Retaining (CR) Triathlon total knee prosthesis (Stryker) was implanted. A femoral and tibial size 5 component with a 13 mm insert were implanted. Initially, 6 weeks after surgery, a functional range of motion and good stability were regained. However, a few months after surgery our patient developed posterolateral knee pain. Imaging by conventional X-rays (figure 1 and 2) and examination of the inflammatory parameters by blood tests did not show any manifestations of peri-prosthetic joint infection or (septic) loosening of the prosthetic components. No additional CT-scan was made since there was no clinical or radiological suspicion of loosening or mal-positioning of the components.


Fig 1: Anterior posterior view of the TKA 5 years after surgery


Fig 2: Lateral view of the TKA 5 years after surgery

Six months after TKA ultrasound (US), showed an inflamed bursa, between the popliteus tendon and posterior tibia. This was treated with a local injection (bupivacaine/triamcinolone), unfortunately without any pain relief. She was referred to the department of sports medicine for stretch exercises guided by a physiotherapist. The patient returned three years after TKA to our outpatient clinic with persistent pain in the posterolateral region of the knee. US showed no signs of tendinitis and a (diagnostic) US guided injection with bupivacaine/triamcinolone in the PT was performed. In contrast to the previous bursal injection, this time all preexisting pain was reduced by the injection. Therefore, we concluded that the pain was most likely attributed to impingement of the PT. In 1,5 years, three US guided PT injections were performed. All showed a good short-term reduction of knee pain. Five years after the primary surgery we recommended surgical transection of the PT, aiming for a long-term benefit. In context of shared decision making, the patient decided that the chance of pain relief outweighed the potential chance of knee instability after transection of the PT. The patient consented that her data, including her radiographic imaging, could be used for publication.

Intervention The procedure was performed while using a tourniquet to minimize blood loss. A 4-cm vertical skin incision was made at the joint line, just posterior to the lateral collateral ligament, as described by Medvecky et al.9 An interval between the short head of the m. biceps femoris and the iliotibial band was opened up. With the knee joint in 90 degrees flexion, the PT was exposed posterior to the lateral collateral ligament (LCL). The PT was not completely visualized due to the overlying lateral collateral ligament, extra care was taken during the lateral release. When inspecting the PT in situ there was visual damage and fibrotic tissue. The PT was released mid-section at the posterolateral side of the knee, no evident retraction along the femoral condyle was seen during the release. The joint capsule and iliotibial tract were closed separately.

Outcome Two weeks and two months after surgery there were no complications and 80% of the pain was relieved. Our patient was able to walk without pain. Her knee showed good function (120/0/0) and stability. The stability of the knee in 30 degrees flexion was less than a 5 mm movement anterior-posterior and less than a 5 degrees movement medial-lateral. After three months our patient was free of pain, and at the final follow up after 12 months she did not show any complications either. Our patient was satisfied and able to function without complaints.

Discussion In total, approximately 20-30% of the patients are unsatisfied after primary TKA, of which a small portion might be contributed by PTI.2,10 Oversized components can shift the popliteus position during a full arc of motion. However, Bonnin et al. also describes that despite a more physiological tracking of undersized components, even correct-sized tibial components can modify popliteal tracking, possibly resulting in PTI.5 This is recognized in our case. In the case of postoperative dorsolateral knee pain and no signs of peri-prosthetic joint infection, loosening or oversized prosthetic components, then impingement of the PT should be considered as a possible cause. Ultrasound has the real-time capability to observe mechanical catching and be effective in the discovery and confirmation of PTI after TKA. US combined with a guided anesthetic injection as diagnostic treatment and steroid injection as potentially therapeutic.11 There is debate about whether PT should be preserved or transected during TKA. Transection may affect gap balancing in flexion and extension, and result in posterior flexion-instability. This was shown in a cadaver trial where cruciate-retaining (CR) and posterior stabilized (PS) prostheses were used, before and after the transection of the PT gaps were measured. The medial gap (in 90 degrees flexion: increase CR 0.8 mm, increase PS 1.4 mm | extension: increase CR 1.7 mm, increase PS 0.9 mm) was significantly increased after PT section in flexion and extension in the CR-TKA group, in the PS-TKA group the flexion gap was only significantly increased in flexion. The lateral gap (90 degrees flexion: increase CR 2.1 mm, increase PS 1.64 mm | extension: increase CR 1.4 mm, increase PS 1.7 mm) was significantly increased both in flexion and extension for the CR-TKA and PS-TKA group.3 Most of the evidence shows that the PT should be preserved during total knee arthroplasty as general functional scores are shown to be lower in patients with an iatrogenic popliteal injury.11

Ghosh et al. state that the PT is crucial to posterolateral stability.4 They compared PS-TKA with the native knee and concluded that in PS-TKA transection of de PT did not substantially generate abnormal knee laxity.4 In our case, a CR primary TKA was implanted. Several studies describe an arthroscopic PT release as a reliable procedure for PTI after knee arthroplasty without compromising knee stability.6,7 Our senior orthopaedic surgeon opted for a minimal open posterolateral PT release to have a better view and so preventing damaging the prosthesis during arthroscopy. Before performing this specific operation, the operation technique was first tested and performed on a cadaver.

Recommendation The current literature on PTI after TKA is limited. PTI as a cause for residual pain after TKA might be underdiagnosed despite extensive literature on additional diagnostics in malfunctioning TKA. In the case of unknown posterolateral knee pain after TKA, PTI could be evaluated as a possible cause by using US imaging combined with US-guided injection with anesthetic as a diagnostic treatment and corticosteroid injection as a potential therapeutic treatment option. In the case of PTI, those injections could relieve the posterolateral knee pain. When injections of the PT are no longer a sufficient treatment option, surgical release of the PT could be considered with reasonable chances of long-term pain reduction. Funding: This study was not funded

Conflict of Interest/Disclosure statement: Author C.R. Quispel declares that he has no conflict of interest. Author S.R. Beekhuizen declares that he has no conflict of interest. Author M.M. Bruin declares that he has no conflict of interest. Author R. Ridder declares that he has no conflict of interest.

Ethical approval: This article does not contain any studies with human participants or animals performed by any of the authors.

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