Most studies about hemi-arthroplasty of hip have focused on clinical aspects. Design features of various implants of hemi-arthroplasty have not been studied extensively. The aim was to investigate the relationships between radiological variables and possible mode of failure in various hemiarthroplasty implants in intracapsular neck of femur fractures.

A retrospective review of 42 hemi hip arthroplasties, Austin Moore and Thompson prosthesis by Biomet, Medical Product Service (Tipsan) and Smit Medimed (SMPL) used in our hospital. Controversy exists between indication for a particular design in an unselected series of patients once excluding the choice of cementing or uncementing the prosthesis. In monoblock prosthesis not only the head-neck region affects the stability but also the stem fit in proximal femur.

Surgeon preference to technique and approach excluded. Premorbidly all patients were mobilising independently. 5 criteria reviewed. 1) head size of prosthesis 2) neck length 3) prosthesis stem shaft angle 4) stem-cortical distance ratio and 5) shape of the femoral canal as classified by Dorr. Head size compared in AP views of involved hip and normal head size compared with that of prosthesis. A difference <2 mm or >3 mm indicative of incorrect size. Neck length measured by the vertical distance from center of head to superior aspect greater trochanter was zero. A range of +/− 5 mm was acceptable. Neck shaft angle with a difference of >5 degrees was indicative of varus position of the stem. Canals of the proximal femoral categorized as a) stove pipe b) champagne c) fluted varieties radiologically. X-ray magnification corrected. All measurements were done on immediate postoperative radiographs.

Stability of various design features of straight stemmed and curved implants are dependant on the anterior bowing angle and canal ratio of femur to prosthesis. A prospective study with CT from selected shapes of the proximal femoral is being carried out. Inappropriate head size as reported by Thompson or neck length was related to incidence of dislocation resulting in failure. Our findings emphasise importance of careful selection of a particular implant design towards the morphology of the femoral canal.

CAN TKR is aimed to improve accuracy in realignment with balanced knee joint.

Variability in the force exerted during tissue tensioning depends on the viscoelastic nature of soft tissues.

Aim: To measure gap balance to assess effectiveness of CAN on ligament balance using gap balancing approach with tibia 1st cut.

Methods: OrthoPilot system with 4.3 software and Statistical evaluation with Testimate Version 6.0, IDV Gaunting Germany with a two sided Wilcoxon-Pratt test (P< 0.05) used simulating errors in extension and flexion gap balance. P1, control with 16 datasets created and P2-P7 (96 case series) was propagated with ±3mm variants in extension and flexion gap both medial and lateral, only varying 1, keeping others constant. Controls fixed: distal transverse plane cut at 0° to femoral mechanical axis in frontal plane and 3°external rotation in sagittal plane. Tibia cut 90° to mechanical axis. Mechanical axis constant at 0° and gap balance at 0 mm. Deviations in gap errors using trigonometrical calculations based on E-Motion femoral implant, size/thickness; 3/7mm and 4/8.5mm with variation of insert size 10/12mm equal to sum of gap and bone cut.

Results: Over tensioning (OT) distal lateral extension gap (DLEG) causes tight distal medial extension gap (DMEG). Under tensioning (UT) DLEG causes loose posterior medial flexion gap (PMFG). UT DLEG causes tight DLEG. Impact factor > 2mm increased PMFG with lateral lift off with only PMFG as variant. Increasing PMFG > 2mm caused lax PMFG. UT even by 1mm PMFG causes error by notching and tight PMFG. A considerable number of errors observed in frontal plane of femur.

Relationships between OT/UT analyzed by Spearman rank ratio p< 0.001.

Conclusions: Change of tissue spreader tension in EG or FG causes improper registration with mismatch in EG/FG/Bone cut. This study provides a baseline to further assess and develop the concept of optimal soft tissue balance as ligaments function properly only with the desired isometry in gap balancing technique.