Risk of sural nerve injury during lateral distal Achilles tendinoscopy: a cadaver study.

BACKGROUND: The risk of damage to cutaneous sensory nerves located near portals has been evaluated for both conventional arthroscopy and extra-articular posterior ankle endoscopy. The objective of the anatomic study reported here was to assess the risk of injury to the sural nerve or lateral calcaneal nerve while using the distal lateral portal for the Achilles tendinoscopy procedure described by Vega et al. in 2008. MATERIALS AND METHODS: We dissected the sural nerve and its branch, the lateral calcaneal nerve, of 13 human cadaver ankles in the prone position. We defined P as the point where the Achilles peritendon was opened during the distal lateral approach used for the study technique. P was adjacent to the lateral edge of the Achilles tendon, 2 cm proximal to the postero-superior edge of the calcaneal tuberosity. T was defined as the attachment site of the most lateral fibres of the Achilles tendon to the postero-superior edge of the calcaneal tuberosity. We evaluated the origin of the lateral calcaneal nerve relative to T and we measured the shortest distances separating P from the sural nerve and lateral calcaneal nerve. RESULTS: A lateral calcaneal nerve was identified in 10 (77%) ankles and originated a mean of 39.1mm (range, 25.0-65.0mm) proximal to T. P was at a mean distance from the sural nerve of 12.3mm (range, 5.0-18.0mm) and from the lateral calcaneal nerve of 6.8mm (range, 4.0-9.0mm). The median difference between these two distances was statistically significant (P=0.002). DISCUSSION: While using the distal lateral portal for Achilles tendinoscopy, the lateral calcaneal nerve is at greater risk for injury than is the sural nerve. LEVEL OF EVIDENCE: Level IV. Anatomic Study.

Cruciate-sacrificing total knee arthroplasty and insert design: A radiologic study of sagittal laxity.

INTRODUCTION: Ultracongruent inserts avoid some of the drawbacks of central spine postero-stabilized inserts. However, early wear has been reported, and may be due to increased sagittal laxity. The principal objective of the present study was to compare sagittal laxity in rotating platform total knee replacements (TKR) according to insert design: ultracongruent versus central spine. The principal hypothesis was that insert design influences global sagittal laxity. MATERIAL AND METHODS: A retrospective comparative study recruited 3 consecutive series of patients treated for primary osteoarthritis of the knee, with a minimum 1 year's follow-up. The UC series comprised 35 knees in 34 patients, receiving a Total Knee Triathlon™ (Stryker Orthopaedics, Mahwah, NJ) TKR with ultracongruent insert, at a mean 2.0 years' follow-up. The UC+ series comprised 36 knees in 34 patients, receiving the BalanSys™ (Mathys Ltd, Bettlach, Switzerland) TKR with ultracongruent insert, at a mean 2.5 years' follow-up; in this model, the anterior edge of the insert is higher than in the UC series ("deep-dish" design). The PS series comprised 43 knees in 40 patients, receiving a Total Knee Triathlon™ (Stryker Orthopaedics, Mahwah, NJ) TKR with central spine posterior stabilization, at a mean 1.5 years' follow-up. The principal assessment criterion was sagittal laxity at 90° flexion as measured by the Telos Stress Device® (Metax GmbH, Hungen, Germany). RESULTS: Sagittal laxity did not significantly differ between the UC and UC+ series: mean 8.2mm (range: 0-19.5mm) and 8.4mm (4.5-15.8mm), respectively. Sagittal laxity in the PS series was significantly less: 1.4mm (0.2-3.9) (P<0.0001). CONCLUSION: Sagittal laxity was greater in ultracongruent than central spine posterior stabilized TKR. This anteroposterior movement may induce polyethylene wear. The ideal degree of sagittal laxity for ultracongruent inserts remains to be determined. LEVEL OF EVIDENCE: IV - retrospective study.