Summary

This original case series aims to describe an uncommon triad of clinical signs in patients presenting with persistent pain and inability to resume physical activities after knee hyperextension trauma, which could be consistent with a partial posterior cruciate ligament (PCL) injury of the posteromedial bundle (PMB).

Abstract

Purpose

This original case series aims to describe an uncommon triad of clinical signs in patients presenting with persistent pain and inability to resume physical activities after knee hyperextension trauma, which could be consistent with a partial posterior cruciate ligament (PCL) injury of the posteromedial bundle (PMB).

Methods

Patient history, clinical examination, arthroscopic findings and investigations of 12 patients (7 males/5 females) who consulted with the senior author are presented for persistent pain after knee hyperextension trauma either in sport or a traffic accident.

Results

Patients had a median age of 18.5 (Q1–3: 16.3–26.0) and a median BMI of 23 kg/m2 (Q1–3: 20–24). The common factors were that they consulted for unresolved persistent pain at a median of 4 months (Quartile 1: 2–Quartile 3: 11 months) after at least one knee hyperextension trauma. All had undergone an MRI (eight patients even two) and medical visits before visiting the institution. In none of them, the cause of their problems could be explained. None of them reported any experience of knee instability.
Gait and clinical examination appeared to be normal for all patients. The injured knee did not display an increased laxity at 90° of flexion. An uncommon triad of clinical signs with the knee close to extension could however be observed: (1) grade 1+ anterior–posterior laxity around 10–20° of flexion with firm end‐point (pseudo‐Lachman sign), (2) grade 1+ tibiofemoral step‐off sign with posterior drawer at 10–20° of flexion and (3) increased knee hyperextension compared to contralateral side. Arthroscopy of eight patients confirmed the pseudo‐Lachman sign with a grade I posterior drawer close to knee extension, normal posterior laxity at 90° of knee flexion and an intact anterior cruciate ligament.

Discussion

Grade 1+ anterior–posterior laxity around 10–20° of knee flexion with a firm end‐point was the trigger to evaluate the knee closer to extension as it may be indicative of a pseudo‐Lachman sign rather than a true positive Lachman test. The step‐off sign, usually performed around 90° of knee flexion, was thus reiterated at 10–20° of flexion. The grade 1+ magnitude supported the fact that the tibia may be posteriorly displaced. In the absence of a positive posterior drawer at 90° and in the presence of a higher hyperextension of the knee compared to the contralateral side, the senior author concluded that a partial tear of the PCL and more precisely of the PMB was to be considered as the latest is known to have a primary role in limiting posterior tibial translation and hyperextension at low flexion angles.

Conclusion

Patients displayed an increased hyperextension and posterior laxity close to knee extension which normalized at 90° of knee flexion. In patients with a history of knee hyperextension trauma associated with persistent pain, inability to resume physical activities, inconclusive MRIs and a standard clinical examination, clinicians should consider extending their investigations with the knee close to extension to identify this clinical triad consistent with a lesion to the PMB of the PCL.