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Clinical lead, Mr Krisztian Sisak
Unicompartmental knee replacement in the ACL deficient knee: revisited

The discussion regarding the treatment of isolated medial compartment severe osteoarthritis (OA) has produced numerous publications and occupies a permanent slot at knee seminars and courses.

A specific subgroup of patients have anterior cruciate ligament (ACL deficient knees with concomitant medial OA. These patients usually present in two distinct groups. Young and active patients (< 55 years) with OA secondary to an ACL deficiency and a second group of somewhat older patients with primary OA with secondary ACL deficiency.

Classic orthopaedic teaching considers ACL deficiency with medial compartment OA to be a contraindication for unicompartmental knee replacement (UKR).1 Historically, the reported early failures of UKRs in ACL deficiency were mainly due to increased wear eventually causing aseptic loosening of the tibial component. Staged or simultaneous ACL reconstruction and UKR has been described as a potential surgical procedure for medial compartment OA secondary to ACL deficiency in the younger patient where joint preservation is not possible.  A recent report of 52 consecutive patients undergoing staged or simultaneous procedures showed excellent results in terms of survivorship (93%) and patient satisfaction (98%).2 Longer term follow-up will help streamline the procedure, as several questions are still not quite clear: one-stage or two-stage procedure, graft choice, femoral and tibial tunnel placement, fixation devices for the graft, mobile or fixed bearing UKR, post-operative rehabilitation, etc.

It is tempting to consider foregoing the long rehabilitation required by an ACL reconstruction but still enjoying the advantages of UKR over a total knee replacement (TKR) such as: decreased surgical tissue dissection, shortened hospital stay, earlier return to preoperative function.  This is especially true for the older patient. Two recent medium term follow-up studies showed equivalent survivorship of UKR in ACL deficient knees if compared with results of similar, matched knees with an intact ACL.3,4 Mobile-3 and fixed-bearing4 UKRs both seem to do well in a selected patient group, who have medial OA, a deficient ACL and have no obvious instability.

Both these retrospective studies from high volume specialist centers come with a caveat: patient selection. Even experienced surgeons would only see a handful of suitable patients yearly, who are clinically and radiologically ideal for a UKR, but are found to have a deficient ACL intraoperatively. In these cases if the patient had no preoperative signs or symptoms of instability, should the surgeon convert to a TKR if he or she finds a non-functional ACL? Certainly not. However, this will be the exception and not the rule.


Mr Krisztian Sisak, Consultant Orthopaedic Surgeon and Senior Lecturer, University of Szeged, Hungary.

November 2014



1.      Engh GA, Ammeen DJ. Is an intact anterior cruciate ligament needed in order to have a well-functioning unicondylar knee replacement? Clin Orthop Relat Res 2004;428:170-3.
2.      Weston-Simons JS, Pandit H, Jenkins C, Jackson WF, Price AJ, Gill HS, Dodd CA, Murray DW. Outcome of combined unicompartmental knee replacement and combined or sequential anterior cruciate ligament reconstruction: a study of 52 cases with mean follow-up of five years. J Bone Joint Surg [Br] 2012;94-B:1216-20.
3.      Boissonneault A, Pandit H, Pegg E, Jenkins C, Gill HS, Dodd CA, Gibbons CL, Murray DW. No difference in survivorship after unicompartmental knee arthroplasty with or without an intact anterior cruciate ligament. Knee Surg Sports Traumatol Arthrosc 2013;21:2480-6.
4.      Engh GA, Ammeen DJ. Unicondylar arthroplasty in knees with deficient anterior cruciate ligaments. Clin Orthop Relat Res 2014;472:73-7.

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