This paper elegantly and convincingly describes a previously unrecognised lesion that of postero-medial capsulo-meniscal rupture. Its true prevalence will need to be established by further studies which will for the moment rely upon the clinical acumen and arthroscopic skills of surgeons until MRI protocols can be developed to demonstrate the pathology, since at present it does not show on standard MRI series.
The diagnosis of ACL rupture is often delayed even when a clear history with a typical valgus external rotation injury is given.1 The diagnosis may not be made by the first treating doctors and of more concern perhaps is that more senior doctors also seem to have difficulty. This may lead to delayed treatment which may compromise the long term outcome and increase the morbidity associated with the injury. That ACL rupture occurs in association with other ligamentous injuries to the same knee is well known.2,3 The need to look for and treat posterolateral corner injuries in ACL deficient knees tears is well described and the presenting symptomatology and findings on clinical examination have been clearly established. This study describes a new association with ACL rupture for which the clinical correlation is as yet unclear.
The fact that postero-medial capsulo-meniscal rupture was noted in the context of a high volume specialist knee unit as an unusual finding on arthroscopy which was not correlated with any particular symptoms suggests that it is not in itself associated with particularly disabling separate or distinct symptoms. It also suggests that the initial clinical signs were not marked,
It is a recognised fact that a careful history and accurate clinical examination are the keys to good diagnosis. This holds true for the ACL deficient knee where careful, trained clinical examination is superior to MRI investigation in demonstrating rotational instability.4 This diagnosis of postero-medial capsulo-meniscal rupture can, it appears at present, only be made by careful clinical examination and in particular by performing a “Dial” test in the supine position to allow clear identification of which tibial condyle is rotating.
That arthroscopic examination of the postero-medial recess by passing the arthroscope into this area through the notch is required to identify the lesion further emphasises the requirement to undertake a systematic, structured and full examination of the knee in all knee arthroscopic procedures.
One of the key messages of this paper is to alert us to the possible presence of what may be taken for apparent posterolateral instability which is in fact postero-medial instability. A misdiagnosis may lead to the performance of an unnecessary reconstruction.
Whilst the lack of particular symptoms associated with this lesion may suggest that further enquiry is not required, this previously unknown associated lesion of the ruptured ACL may explain some of the variability in symptoms in the un-repaired patient or may be associated with a poorer outcome in the reconstructed patient.
Clearly further studies of incidence and to correlate the condition with clinical symptoms and outcomes both in isolation in the unreconstructed ACL-deficient patient and after reconstruction are required. The significant learning point from this study is to perform the “Dial” test in the supine position and to carefully evaluate which tibial condyle rotates.
1. Bollen SR, Scott BW. Rupture of the anterior cruciate ligament: a quiet epidemic? Injury 1996;27:407-409.
2. Fridén T, Erlandsson T, Zätterström R, Lindstrand A, Moritz U. Compression or distraction of the anterior cruciate ligament: variations in the injury pattern in contact sports & downhill skiing. Knee Surg SportsTtraumatol Arthrosc 1995;3:144-7.
3. Rose N, Gold S. A comparison of accuracy between clinical examination and magnetic resonance imaging in the diagnosis of meniscal and anterior cruciate ligament tears. Arthroscopy 1996;12:398-405.
4. Järvinen M, Natri A, Laurila S, Kannus P. Mechanisms of anterior cruciate ligament ruptures in skiing. Knee Surg Sports Traumatol Arthrosc 1994;2:224-8.
Shaw DL, Consultant Orthopaedic Surgeon
Bradford Teaching Hospitals (UK)