Abstract
Introduction
Despite the multiple patho-aetiological basis of Hallux valgus (HV), corrective osteotomy is a common and globally performed orthopaedic procedure. Over-correction of the inter-metatarsal angle (IMA), however, is not without consequence. Through increased joint pressures, over-correction may predispose to joint degeneration. Hypothesizing that over-correction leads to an increase in intra-articular joint pressures, we constructed a mechanical simulation of the 1st metatarsal-phalangeal joint.
Methods
The vector forces of Flexor Hallucis Longus, Extensor Hallucis Longus, Extensor Hallucis Brevis and Adductor Hallucis, acting upon the 1st proximal phalanx were simulated with tensioned weighted rope. A Foley catheter balloon inflated to 1.5ml, simulated intra-articular distractive vector forces. The joint was freely mobile.
At 5° IMA intervals from 10° valgus to 15° varus, intrarticular pressures were recorded using a contact pressure (Graseby™, Hertfordshire, UK) transducer attached to a calibrated manometer (Digitech Instruments™, Ulhasnagar, India). At each angle, measurements were repeated five times with removal and recalibration of the pressure monitor after each measurement.
Results
A decline and subsequent increase in mean pressure was observed at each 5° interval from 10°valgus to neutral and then to 15° varus (mean±s.d.; 48.02±5.67, 24.72±1.01, 12.34±0.84, 18.96±2.46, 32.88±5.06, 42.92±4.99 milibar for 10°, 5° valgus, neutral, 5°, 10°and 15° varus IMA). One-way analysis of variance with post-hoc Tukey multiple comparison test revealed a significant increase in pressure from neutral and 5° valgus to 10° and 15° varus (p< 0.05).
[First Metatarsal Phalangreal joint pressures]
Conclusion
This is the first description demonstrating increases in intrarticular pressures as the IMA tended from 5° to 15° varus, replicating inatrogenic Hallux Varus iatrogenically produced through osteotomy and over-correction of the IMA. Over-correction and increased intrarticular joint pressure may have an aetiological basis to post-operative 1st MTPJ degeneration. Over-correction is not a benign entity requiring consideration in Hallux Valgus corrective osteotomy.
