Anatomical referencing, component positioning, limb alignments and correction of mechanical axes are essential first steps in successful computer assisted navigation. However, apart from basic gap balancing and quantification of ranges of motion, routine navigation technique usually fails to use the full potential of the registered information. Enhanced dynamic assessment using an upgraded navigation system (Brainlab V. 2.2) is now capable of producing enhanced ‘range of motion’ analysis, ‘tracking curves’ and ‘contact point observations’.

‘Range of motion analysis’ was performed simultaneously for both tibio-femoral and patella-femoral joints. Other dynamic information including epicondylar axis motion, valgus and varus alignments, antero-posterior tibio-femoral shifts, as well as flexion and extension gaps were simultaneously stored as a series of ‘tracking curves’ throughout a full range of motion. Simultaneous tracking values for both tibiofemoral and patellofemoral motion was also obtained after performing registration of the prosthetic trochlea. However, there seems to be little point in carrying out such observations without fully assessing joint stability by applying controlled force to the prosthetic joint.

Therefore, in order to fully assess ‘potential envelopes of motion’, observations have been made using a set of standardised simple dynamic tests during insertion and after final positioning of trial components. Also, such tests have been carried out before and after any necessary ligament balancing. Firstly, the lower leg was placed in neutral alignment and the knee put through a flexion-extension cycle. Secondly the test was repeated but with the lower leg being placed into varus and internal rotation. The third test was performed with the lower leg in valgus and external rotation. Force applied was up to the point where resistance occurred without any gross elastic deformation of capsule or ligament in a manner typical of any surgeon assessing the stability of the construct. Also a passive technique of using gravity to ‘Drop-Test’ the limb into flexion and extension gave useful information regarding potential problems such as blocks to extension, over-stuffing of the extensor mechanism and tightness of the flexion gap. All the definitive tests were performed after temporary medial capsular closure.

Ten total knee arthroplasties have been studied using this technique with particular reference to the patterns of instability found before, during and after adjustments to component positioning and ligament balancing. Marked intra-operative variation in the stability characteristics of the trial implanted joints has been quantified before correction. These corrections have been analysed in terms of change in translations, rotations and contact points induced by any such adjustments to components and ligament. Certain major typical patterns of instability have begun to be identified including excessive rotational and translational movements. Instability to valgus and external rotational stress was found in two cases and to varus and internal rotational stress in one case before correction. In particular, surprising amounts of edge loading in mid-flexion under stress testing has been identified and corrective measures carried out. Reductions in paradoxical tibio-femoral antero-posterior motion were also observed. Global instability and conversely tightness were also observed in early stages of surgery. Adjustments to component sizes, rotations, tibial slope angles and insert thickness were found to be necessary to optimise range of motion and stability characterisitics on an almost case-by-case basis. Two cases were identified where use of more congruent or stabilised components was necessary. Observation of quite marked loss of contact between tibia and femur was seen on the lateral side of the knee in deep flexion in several cases. Patellar tracking was also being observed during such dynamic tests and in two cases staged partial lateral retinacular releases were carried out to centre patellar tracking on the prosthetic trochlea.

Although numbers in this case series are small, it has been possible to begin to observe, classify and quantify patterns of instability intra-operatively using simple stress tests. Such enhanced intra-operative information may in future make it possible to create algorithms for logical and precise adjustments to ligaments and components in order to optimise range of motion, contact areas and stability in TKR.

Introduction: The proximal femoral nail antirotation (PFNA) system is a cephalomedullary device originally designed to contend with the challenge of unstable tro-chanteric femoral fractures with the novel helical blade component aimed at limiting femoral head limiting cutout. We demonstrate its use in a variety of cases.

Methods: This is a prospective study of 370 consecutive patients treated with short and long PFNA systems at a single center with 1-year follow-up. The device was used for unstable trochanteric femoral fractures (AO-classification 31. A.2 and A.3), prophylactic and definitive fixation of pathological fractures and high energy femoral fractures for a wide age range (19–101 years). Clinical outcome involved assessment of general mobility & function, operative and post-operative parameters & complications. Radiological outcome involved assessment of blade tip-apex distance, nail tip-femoral scar distance and distal locking configurations.

Results: 17% died within the follow-up period. 72% achieved their pre-trauma mobility status and nearly all fractures healed within 6 months including those in over 85 years. Of 18 problematic cases, serious complications included deep infection, loss of proximal reduction, ipsilateral femoral shaft fracture and periprosthetic supra-condylar fracture. There were no cases of acetabular penetration or blade cut-out. Short PFNA was associated with the majority of femoral shaft fractures and the only significant finding regarding instrumentation.

Discussion: This study supports long PFNA design theory demonstrating adequate purchase in the femoral head-neck zone, shown by lack of cut-out. Positive results have been demonstrated in a variety of cases making it a useful option in fractures in all ages and indications alongside unstable trochanteric configurations.