This is a plain-English translation of the academic paper above, prepared for patients, referring clinicians, and other non-specialist readers. It preserves the structure of the original paper while removing technical jargon. For the full clinical paper, follow the PubMed or DOI links.
Background
What happens inside the knee when a long metal rod (a retrograde femoral nail), inserted up the thigh bone from below to fix a fracture, is left sticking out a few millimetres into the knee joint — rather than being seated flush.
Rationale
A common cause of pain after this kind of surgery is the nail being “proud” — sitting slightly too high in the bone, so its tip sits inside the knee joint rather than just below the surface. The painful structures it bumps into have not been clearly mapped out before.
Results
In 15 cadaveric knees, a nail left 10 mm proud impinged on the front edge of the inner meniscus near full extension and on the underside of the kneecap during deeper bending in every case. Even at 5 mm proud, the nail still caught on the meniscus and on the attachment of the anterior cruciate ligament. In other words, even a small misjudgement of nail depth produces internal contact during normal knee movement.
Implications
This study underlines how exact the surgeon needs to be when seating the nail — even a few millimetres too high can produce ongoing knee pain and damage. For a patient with knee pain after this type of surgery, a check on the nail position is a sensible first step.
Source: Clement H, Heidari N, Kosuge D, Grechenig W, Tesch NP, Weinberg AM. Anatomical structures at risk with the proud retrograde femoral nail.. Archives of orthopaedic and trauma surgery 2011;131(11):1539-44. doi:10.1007/s00402-011-1347-9
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