Partial replacement of the meniscus of the knee using a biodegradable scaffold

The menisci are semi-lunar wedge-shaped fibrocartilaginous structures which act as shock absorbers, spreading the load on the articular surfaces of the knee.

The menisci can be damaged (often a tear) as a result of acute injury or degeneration, which may cause pain and/or locking of the knee. It is believed that meniscal damage is associated with a higher risk of knee osteoarthritis in the longer term. Minor meniscal damage can be treated conservatively (including rest and physical therapies). For more severe cases, treatment usually involves removal of the damaged part of the meniscus (partial meniscectomy).

Meniscal repair is possible only in a minority of patients. This depends on the proximity of the damage to the peripheral vascular region of the meniscus (where good blood supply allows meniscal healing), the pattern of the damage and whether there is damage to other knee joint structures.

Implantation of a scaffold for partial replacement of the meniscus of the knee aims to support the body's own physiological pathways for healing by providing a 3-dimensional matrix for cell adhesion and vascular ingrowth, when attached to the vascular portion of the meniscus. In the short term, the procedure aims to restore the load-bearing and shock-absorbing functions of the damaged meniscus, contributing to pain relief and restoring functional mobility. In the long term, it aims to lower the risk of osteoarthritis and the need for further operations. A strict rehabilitation regime is usually employed after the procedure, which may include several weeks of restricted weight bearing and temporary bracing to limit knee movement.

The procedure may be done with the patient under general or regional anaesthesia. Using an arthroscope, damaged sections of the meniscus are excised, leaving a residual meniscal rim in the vascular zone. The size of the defect is measured and the implant is trimmed to match it. The implant is then introduced into the joint via one of the portals and sutured to the remaining meniscal rim. This may require extra skin incisions to provide sufficient access.

The types of scaffolds available for this procedure include those made of synthetic polyurethane and of collagen derived from animal sources.

A randomised controlled trial (RCT) of 311 patients divided patients into two groups, depending on whether they had prior surgery on the affected meniscus. Each group was randomised to treatment by partial replacement of the meniscus with a biodegradable implant or to partial meniscectomy alone. Pain scores were reported as a mean change from baseline (assessed at rest, during activities of daily living and at the highest level of activity, on a visual analogue scale; 0 to 100, higher score indicates greater pain) at mean follow-up of 59 months. The first group of 157 patients had no prior surgery on the affected meniscus. Patients treated by the procedure (n=75) had a mean pain score of 16 compared with 21 for those treated by partial meniscectomy (n=82; reported as not significant, p-values not reported). The second group of 151 patients, who had had prior surgery on the affected meniscus (85 treated by the procedure and 69 treated by partial meniscectomy) had mean pain scores of 18 for both groups (reported as not significant, p-values not reported).

An RCT of 60 patients, which included 30 patients treated by the procedure and high tibial osteotomy (there was a high dropout rate in the comparator arm of tibial osteotomy alone) reported that the 23 patients followed for 8 to 18 months had Lysholm scores (0 to 100, higher score corresponds to better function) which improved from a baseline of 65 to 94 (p-value not reported).

In a case series of 52 patients treated by partial replacement of the meniscus with a polyurethane scaffold, treatment failure (defined as an additional surgical procedure on the involved meniscus) was reported in 15% (8 of 52) of patients (treatment failure related to infection was excluded) and the overall treatment failure was 17% (9 of 52). Three cases were definitely related to the implant, 3 were not related to the implant, 1 was possibly related to the implant, 1 was unknown and 1 treatment failure (infection) was not related to the implant. Timing to the need for further intervention ranged from 1 week to 24 months.

A non-randomised comparative study of 33 patients treated by partial replacement of the medial meniscus (n=17) or by partial medial meniscectomy (n=16) reported mean quality of life scores measured by SF‑36 physical health and mental health indices (scale of 0 to 100, higher score indicates better functioning). For the SF‑36 physical health index, scores were 54 and 44 for the implant and the partial meniscectomy groups respectively, at a mean follow-up of 11 years (p=0.026). For the mental health index, scores were 55 and 44 for the implant and the partial meniscectomy groups respectively at mean follow-up of 11 years (p=0.004).

The RCT of 311 patients reported reoperation rates, defined as an additional surgical procedure (outside the protocol) on the knee as a result of disabling or persistent pain and/or mechanical symptoms that could possibly involve the meniscus. The reoperation rates were 10% and 23% for the implant and the partial meniscectomy groups respectively, at 5 years (denominators not reported; significance not reported). Reasons for reoperation included pain, swelling and instability.

The specialist advisers listed the following key efficacy outcomes: pain reduction, functional improvement, reduction in risk of further degeneration of the articular cartilage lining of the knee, early failure (further surgery) and early failure (symptoms or patient-related outcome measures).

Dislocation of the implant was reported in 1 patient out of 30 treated by partial replacement of the meniscus combined with high tibial osteotomy in the RCT of 60 patients. The implant was removed but the timing of this was not reported.

Implant failure (defined as infection caused by the collagen implant or mechanical failure of the implant) was reported in 8% (2 of 25) of the patients in a case series of 25 patients during follow-up of 10 to 13 years. Postoperative infection (unrelated to the polyurethane scaffold) was reported in 1 patient in the case series of 52 patients at 1 week after the index surgery (resolved with treatment; no further details reported).

Swelling, effusion and redness were reported in 4 patients treated by the procedure and in 1 patient treated by partial meniscectomy in the RCT of 311 patients (timing of assessment was unclear; denominator not reported). Knee swelling was reported in 32% (7 of 22) of the patients in the case series of 25 patients (timing of assessment was unclear; further details not reported).

The specialist advisers listed the following theoretical safety outcomes: reaction to foreign material, lack of repair or healing, with subsequent tearing or displacement, infection or standard related risks for any knee surgery operation.

The committee noted the lack of clear criteria for patient selection for partial replacement of the meniscus of the knee using a biodegradable scaffold. It also noted that there are two main patient groups, young active patients and older patients with meniscal degeneration. It considered that the needs and outcomes of these two groups may be different.