What did the study look at?
Chronic patellar instability involves repeated dislocation of the kneecap and affects quality of life. It is often associated with a shallow groove in which the kneecap runs (the trochlea), insufficiency of the ligament that holds the kneecap from the inner side (the medial patellofemoral ligament, MPFL) and an outward-placed shin-bone tubercle. These patients are also more likely to have symptomatic cartilage damage.
A groove-deepening operation (trochleoplasty) may not be appropriate in patients with advanced kneecap-joint arthritis. The article describes a combined approach used in such a patient.
How was it done?
This is a surgical technique article with a video. The patient was a 24-year-old woman with recurrent instability of the left knee and pain on walking and using stairs, who had undergone a tibial tubercle osteotomy at age 12 and trochleoplasty with MPFL reconstruction at age 20. Imaging showed a kneecap height (Caton-Deschamps index) of 1.3, a sulcus angle of 143.5 degrees, a tubercle-to-groove distance of 22.85 mm and severe cartilage softening. Because of advanced arthritis, trochleoplasty was not considered suitable.
- Groove (trochlea): the patient's groove surface was removed with a saw, and a shell-shaped bone-and-cartilage graft (osteochondral allograft) prepared from a fresh donor thigh bone was fitted and fixed with four headless screws. Bone marrow aspirate concentrate taken from the patient's pelvis was applied to the underside of the graft.
- Kneecap: the damaged area on the back of the kneecap was reamed to 18 mm and a cylindrical allograft was press-fitted without screws.
- Alignment: the shin-bone tubercle was cut again and moved inwards (revision tibial tubercle osteotomy), and the MPFL was reconstructed with a semitendinosus allograft.
After surgery, no weight is borne on crutches for the first 6 weeks, progressing to full weight-bearing at 6-8 weeks. Normal pain-free walking is expected at around 12 weeks but may be delayed because of the complexity of the procedure.
What did it find?
The article does not report this patient's postoperative results. In the discussion, the authors cite earlier work: a review of 129 patients given osteochondral allografts in the kneecap joint found mean graft survival of 87.9% at 5 years and 77.2% at 10 years. They note that only one study has reported clinical outcomes of a bipolar graft technique for trochlear dysplasia.
The authors' conclusion
The authors state that a shell osteochondral allograft can address significant trochlear dysplasia better than cylindrical grafts and can recreate the joint surface and groove at the same time in people with advanced arthritis. They suggest that surgeons treating young patients with extensive kneecap-joint arthritis and chronic instability may find this approach useful to restore the joint surface and minimise the need for total knee replacement at such an early age.
Limitations
- The technique needs a large graft, and because the graft is foreign to the body there is a risk of incomplete integration.
- Without saline during bone cutting, the risk of heat damage to the bone and poor healing increases.
- A poor curvature match between donor and recipient may lead to worse outcomes.
- Literature on using osteochondral grafts together with patellar instability is limited.
Reference
Kerzner B, Gürsoy S, Dasari SP, Fortier LM, Yanke AB, Chahla J. (2022). Trochlear Osteochondral Shell Allograft Technique to Treat Trochlear Dysplasia in the Setting of Chondral Damage and Chronic Patellar Instability. Arthroscopy Techniques, 11(2), e241-e249. Licence: CC BY-NC-ND 4.0.
DOI: 10.1016/j.eats.2021.10.014
Free full text: PubMed Central (PMC8821720)
This article summarises a published scientific paper for general information; it does not replace an examination or a personal medical assessment. Please consult your doctor about your symptoms.
