Approach to Hip Arthroplasty with Femoral Deformity
When conceptualizing these deformities, think about them in terms of SITE, GEOMETRY, and ETIOLOGY.
– Site: GT, neck, metaphysis, diaphysis
– Geometry: torsional, angular, translational
– Etiology: developmental, metabolic, fracture, osteotomy
– these all require careful preoperative planning and templating
– beware the sagittal plane deformities – high risk of fracture!
– anticipate the need for special implants in terms of size and modularity, and the need for special approaches
Greater Trochanter – the Over-Hanging Trochanter or High Riding Trochanter
– the overhanging trochanter can make access to canal difficult – risk breaking it off with the reaming
– the high riding trochanter can cause impingement and instability
– probably best to osteotomize it and reattach it
Femoral Neck – Varus, Valgus, or Torsional Deformity
– if varus and short – a regular implant will restore length
– if varus and not short – may need special implants with increased offset to avoid overlengthening
– if valgus – beware the overhanging trochanter, and the medial metaphysis may be small, requiring special implants
– if severe torsion – matching the anteversion of the patient may lead to significant internal rotation contracture or instability. Cemented or fully porous coated prosthesis enable you to dial in the anteversion as you wish. Proximally coated prosthesis do not allow this; Consider using a left implant for right to retrovert the neck. Finally, consider derotational femoral osteotomy. Modularity here can be useful (eg. SROM)
– if cementing, make sure the implant fits and can achieve a good cement rim within the given geometry
– if uncemented, can bypass the weird proximal geometry
– modularity may be helpful – eg . SROM – to match the weird proximal geometry with the distal canal
– if severe enough, be prepared for a metaphyseal osteotomy – these can be hazardous, as they leave a very small proximal piece (unlike a subtrochanteric osteotomy) which can fracture or be devascularized
– if distal enough and will not effect limb alignment, ignore
– may need osteotomy – if so, beware of using cement (will in all likelihood extrude into the osteotomy site)
– if doing osteotomy, probably safest to go with extensively porous coated stems with distal fixation – the stem serves to fix the osteotomy site; may use cortical onlay struts if you want.
– consider the need to do a two stage procedure – first stage, osteotomize and fix; second stage once the bone has healed.