LESIONS OF THE SAPHENOUS NERVE AND ITS INFRAPATELLAR BRANCH AS A CAUSE OF PERSISTENT KNEE PAIN

Abstract

Purpose of Study: To further study a group of patients with characteristic features presenting with significant, perisistent, and seemingly hard to diagnose and so treat, knee pain.

Methods/Results: 16 cases were collected. The was no association with age. 8 cases were sent as a second opinion.

• Causation: 7 cases:direct trauma [5: associated with MCL tears (1 chronic overload from triple-jump),1:a blow to front of knee, 1:chronic from kneeling]

• 4 cases: Knee replacement- related [irritation from osteophyte 1; implant-related 3]

• 3 cases: irritation from medial meniscal sutures [2: Fast-Fix; 1: in:out]

• 1 case: surgery induced neuroma in arthrotomy wound

• 1 case: irritation by an enlarging cyst

In all cases the time to make the diagnosis was prolonged. All had pain, which on close questioning was ‘neuritic’ [burning] in approximately 2/3. It was exceedingly well localized in all. Altered sensation in the appropriate distribution was noted by the patient in 3 cases, but shown in 5 cases on examination. A positive Tinel test was present in all cases.

In approximately half of cases ultrasound plus diagnostic injection of local anaesthetic [+/− steroid] was useful. However 15 of the 16 came to surgery in which a neurolysis or removal of neuroma, in 3 cases, [all confirmed on histology] was undertaken plus the underlying causative factor dealt with eg excision of osteophyte or scar. One case settled [90% better according to patient] after ultrasound-guided injection of a prepatellar bursa which was irritating the infrapatellar branch of the nerve. Of the 15 who had had surgery 12 had complete resolution of symptoms.

Conclusion: Although a relatively uncommon this scenario is worth considering as a cause of significant morbidity, with a good outcome from treatment in most cases. The presentation is of persistent very well localized troubling pain with marked tenderness, and a positive Tinel test.