BLOG: Preserve knee joint, lower extremity alignment using novel meniscus implant
Click Here to Manage Email Alerts
This blog reviews the function and importance of menisci in protecting articular cartilage.
The authors discuss biomechanical changes in the articular cartilage in a meniscal-deficient varus knee and review possible interventions, including a meniscal implant called the NUsurface. They present a case study of a patient enrolled in the Verifying the Effectiveness of the NUSurface System (VENUS) Clinical Study who had a NUsurface implant (Active Implants) and review the outcome. The authors conclude the implant may be a bridge between symptomatic patients who have meniscal-deficient medial compartments/varus knees prior to arthroplasty.
Sam Dyer, PA-C
President, Physician Assistants in Orthopaedic Surgery
Menisci play a critical role in the knee joint by providing load distribution, shock absorption and joint congruency. When injured, knee biomechanics are altered and the joint is disrupted. While conservative treatment exists, many patients require a meniscectomy due to mechanical symptoms and pain.
Studies have shown up to 76% of patients with a prior meniscectomy have persistent or recurrent pain. Conservative treatment following meniscectomy includes intraarticular injections, unloading braces and physical therapy. These interventions provide some symptom relief, but do not alter the underlying disease state. This subjects patients to an increased risk for osteoarthritis.
An increase in articular cartilage degeneration, joint space narrowing and progressive malalignment become more concerning in the malaligned extremity. A varus extremity shifts the mechanical axis medially, increasing the load to the medial compartment and the risk of OA. Lee and colleagues reported a preoperative varus alignment was a significant risk factor for the conversion of a total knee arthroplasty in patients with medial meniscus tears treated with arthroscopy.
The NUsurface is a synthetic polymer implant that mimics the physical characteristics of a natural meniscus. It is under review by the FDA. Previous studies have demonstrated the implant reestablishes normal load distribution across the medial compartment and prevents contact between opposing cartilage surfaces following partial medial meniscectomy. However, the impact of the implant on lower limb alignment has yet to be investigated.
Patient information
A 40-year-old male heavy machinery operator presented to the clinic with a chief complaint of bilateral medial compartment knee pain. The left knee had two prior arthroscopies and essentially a subtotal meniscectomy status. The right knee never had surgery. The patient’s complaints were similar in both knees – significant medial compartment pain and exacerbated with weight-bearing. On physical exam, bilateral knees demonstrated no ligamentous instability, obvious effusions or specific meniscus signs. Long-leg weight-bearing alignment radiographs demonstrated the left knee in mild varus alignment of 3.6° with minimal OA changes of the medial compartment.
An MRI demonstrated an essential subtotal medial meniscus resection with intact anterior posterior root attachments and a peripheral rim of tissue. There was also minor chondral thinning of the medial compartment consistent with the weight-bearing radiographs.
Right knee radiographs showed minimal varus angulation of 1.6°. An MRI of the right knee showed tearing of the posterior horn and body of the medial meniscus, as well as mild thinning of the medial compartment articular cartilage.
The patient fit enrollment criteria and was randomized to the study group of the FDA -approved VENUS Clinical Study for the left knee. The medial meniscus implant was performed using an arthroscopic-assisted technique.
Initial arthroscopic review confirmed an absence of full-thickness cartilage defects. The meniscus remnant was prepped with stable peripheral vertical borders and the implant was inserted through a medial incision. The right knee was treated with conservative measures, such as strengthening, weight loss, intra-articular injections and bracing.
The patient was followed rigorously with serial MRIs and radiographs, including long-leg alignment series. The patient’s function and pain were evaluated using the KOOS, IKDC and Western Ontario Meniscal Evaluation Tool (WOMET).
The patient excelled in his recovery. At the 1-week mark, he had significant improvement in knee functional scores and full range of motion. A protocolled MRI showed the implant in a stable position.
Three years later, the right knee deteriorated, and its exam became more pronounced with a positive McMurray sign, positive flexion pinch test and medial joint line tenderness. Early palpable osteophytes of the medial compartment and pseudo laxity from medial joint narrowing at 30° of flexion were noted. Alignment radiographs demonstrated progression of medial compartment narrowing and varus alignment of the knee. An MRI showed advancement of the patient’s medial meniscus tear with moderate medial compartment articular cartilage thinning, and question for a full-thickness articular cartilage defect. A partial medial meniscectomy and an extensive chondroplasty were performed. As expected after the meniscectomy, the patient had definite improvement of mechanical symptoms but had persistent medial compartment pain.
Since the arthroscopy, the patient has undergone various rounds of viscosupplementation, which has provided minimal relief. The patient is in the process of scheduling a right knee medial UKA.
Discussion
Menisci play a vital role in the prevention of articular cartilage degeneration. From a biomechanical standpoint, contact pressures felt by the articular cartilage are increased and knee mechanics are altered following meniscus resection. A meniscus-deficient knee in the setting of varus alignment displaces the weight-bearing axis through the knee, increasing the stress that the medial compartment endures. This leads to progressive degenerative changes, malalignment, pain and decreased function. Unfortunately, a large proportion of meniscus tears require partial or subtotal meniscectomy regardless of these known consequences.
Limited treatment options for persistent pain following meniscectomy include meniscal allograft transplant, UKA or TKA. However, meniscal allograft transplants have a high failure rate in patients older than 35 years and arthroplasty revision is seen up to 35% in patients younger than 60 years.
In this case study, the patient’s right knee, treated with conservative interventions and a meniscectomy, continued to be a source of pain. The right knee classically demonstrated progression of articular cartilage deterioration, joint space narrowing and increased varus malalignment for 6 years. In contrast, the implant alleviated pain, restored joint function and preserved the left knee alignment. Serial full-length weight-bearing radiographs document these findings throughout the trial.
Conclusion
Preventing malalignment and articular cartilage destruction of the joint post-meniscectomy is critical for patient satisfaction, knee biomechanics and delaying arthroplasty. The implant may serve to bridge the gap between partial medial meniscectomy and arthroplasty in symptomatic patients. This finding provides insight to the innovative aspect of managing meniscus tears. It also encourages a retrospective alignment analysis of patients enrolled in the VENUS Clinical Study.
References:
Bayliss LE, et al. Lancet. 2017;doi:10.1016/S0140-6736(17)30059-4.
Chatain F, et al. Arthroscopy. 2003; doi:10.1016/s0749-8063(03)00735-7.
Fairbank, TJ. J Bone Joint Surg Br. 1948;30B:664-670.
Kim C, et al. Knee Surg Sports Traumatol Arthrosc. 2020;doi:10.1007/s00167-020-05905-w.
Lee BS, et al. Am J Sports Med. 2019;doi:10.1177/0363546518819225.
McKeon BP, et al. Orthop J Sports Med. 2020; doi:10.1177/2325967120952414.
Paradowski PT. Osteoarthritis and Cartilage. 2016;24:794-800.
Petty CA, et al. Arthroscopy. 2010;doi:10.1016/j.arthro.2010.08.016.
Rao AJ, et al. Ortho Journal Sports Med. 2015; doi:10.1177/2325967115611386.
Seedhom BB, et al. Eng Med Biol. 1979;8:220-228.
Sheehy L, et al. Osteoarthritis Cartilage. 2011;19:58-64.
Shemesh, M, et al. Biomech Model Mechanobiol. 2020;doi:10.1007/s10237-020-01323.
Tanamas S, et al. Arthritis Rheum. 2009;doi:10.1002/art.24336.
Tetsworth K, et al. Orthop Clin North Am. 1994;25:367-377.
Van Der Straeten C, et al. PLoS One. 2016;doi:10.1371/journal.pone.0156183.
Willinger L, et al. Knee Surg Sports Traumatol Arthrosc. 2020;doi:10.1007/s00167-019-05654-5.
Yoon KH, et al. Sports Traumatol Arthrosc. 2013;doi:10.1007/s00167-012-2261-6.
Collapse