In a study by Dickstein, one-third of total knee patients were not satisfied even though they were all thought to have had successful results by their orthopaedic surgeons. Noble and Conditt's study showed 14% of patients dissatisfied with their outcome with more than half expressing problems with routine activities of daily living. This occurs despite improvements in instrumentation to obtain proper alignment and implants with excellent kinematics and wear characteristics. Perhaps this dissatisfaction is a result of subtle soft tissue imbalance. Soft tissue imbalance can result in almost a third of early TKR revisions. Soft tissue balancing techniques still rely on subjective feel for appropriate ligamentous tension by the surgeon. Surgical experience and case volume play a major role in each surgeon's relative skill in balancing the knee properly.

New technology of “smart trials” with embedded microelectronics, used in the knee with the medial retinaculum closed, can provide dynamic, intraoperative feedback regarding quantitative compartment pressures and component tracking. While visualising a graphical interface, the surgeon can assess the effect of sequential soft tissue releases performed to balance the knee. These smart trials also have imbedded accelerometers used to confirm that one is balancing a properly aligned knee and to provide the option of doing small bony corrections rather than soft tissue releases to obtain balance.

A multi-center study using smart trials is demonstrating dramatically better outcomes at six months.

Most orthopaedic surgeons believe that total knee replacement has superb patient outcomes. Long-term results are excellent, with one study showing 15 year survivorship of 97%. However, our objective assessments of our patients' results are greater than patients' subjective assessments. In a study by Dickstein of total knee patients, one-third were not satisfied even though they were all thought to have had successful results by their orthopaedic surgeons. Noble and Conditt's study showed 14% of patients dissatisfied with their outcome with more than half expressing problems with routine activities of daily living. We are puzzled by this patient dissatisfaction since radiographs usually show normal component alignment and positioning. Perhaps some of these patients have subtle soft tissue imbalance and kinematic maltracking.

Excellent aligned bone cuts can be expected with modern instrumentation, especially if patient specific cutting instruments or computer navigation are used. However, inadequate instrumentation exists for soft tissue balancing. It is usually based on feel and visual estimation. Soft tissue balancing techniques are difficult to teach and perform by a less experienced surgeon.

Smart trials with load bearing and alignment sensors, which can be used with the medial retinaculum closed, will demonstrate the total knee kinematics and quantify soft tissue balance. Graduated soft tissue balancing can be performed while visualising changes in compartment loads. Studies are ongoing with smart trials to establish evidence-based clinical algorithms for soft tissue balancing and document the effects of these techniques on patient satisfaction and long-term outcome.

A study by Harris reported a 40% incidence of femoral and acetabular dysplasia in routine idiopathic osteoarthritic patients. Fortunately most are minimally dysplastic requiring little modification from standard total hip surgical techniques. However, as the degree of dysplasia increases numerous anatomic distortions are present. These include high hip centres, relative acetabular retroversion, soft bone in the true acetabular area, increased femoral neck anteversion and relative posteriorly positioned greater trochanters, metaphyseal/diaphyseal size mismatch, and small femoral canals. Total hip replacements for these patients have known higher risks for earlier loosening, dislocation, and neurovascular injuries.

Use of medialised small uncemented acetabular components placed in the anatomic acetabulum, modular uncemented femoral components, and diaphyseal rotational and shortening osteotomies has become the standard method of treatment. In 2007, we reported our experience with this technique in 23 cases utilising a subtrochanteric femoral osteotomy with a 5–14 year follow-up. There were 4 Crowe I, 3 Crowe II, 5 Crowe III, and 11 Crowe IV cases. All osteotomies healed. There were no femoral components revised. One acetabular component was revised for a recalled component. 3 acetabular liners were revised for wear (2 were very small cups with 4.7 mm poly thickness). 4 patients sustained dislocations, with 2 closed and 2 open reductions. There were no neurovascular injuries.

The Crowe classification is commonly used to pre-operatively classify the degree of dysplasia. However, there are large variations in these anatomic distortions within each class, so it is difficult to pre-operatively plan the acetabular component size needed and if one will need to do shortening and/or rotational osteotomy. So the surgeon needs to bring their entire bag of tricks and tools for these surgeries.

Pre-operative planning in revision total knee replacement is important to simplify the surgery for the implant representative, operating room personnel and the surgeon. In revision knee arthroplasty, many implant options can be considered. This includes cemented and cementless primary and revision tibial and femoral components, with posterior cruciate retention or resection, and either with no constraint, varus/valgus constraint, or with rotating hinge bearings. One may also need femoral and tibial spacers or bulk allograft. It is important to pre-operatively determine which of these implants you may need. If I ask my implant representative to “bring everything you've got, just in case,” I will get 23 pans of instruments, 24 bins of implants composed of 347 boxes of sterile implants, and chaos for everyone.

Occasionally, one may not need to revise all components, so the surgeon needs to be familiar with the implants they are revising. Consider having some or all compatible components available.

Most revision knee implants can be conservatively cemented with diaphyseal engaging press-fit stems. Most importantly, pre-operative physical examination and radiographs are used to determine the status of the collateral ligaments, so that the appropriate constrained implants will be available at surgery. Radiographs will also show the amount and location of bone loss. This will determine if revision type implants, spacers or bone graft will be needed. Radiographically, one can determine the appropriate joint line position relative to the existing femoral component to simplify the surgery. Excellent pre-operative planning will minimises the need to bring in an excessive number of instruments and implants. It will help assure that the patient has a stable revision knee and simplify the surgery for all participants.

Frequently surgeons performing total knee replacements are faced with the dilemma of whether to notch the anterior cortex or overhang the medial and/or lateral cortices when implanting the femoral component. This is almost always seen in female patients. There is also a higher incidence of patellar alignment problems in female patients post total knee replacement. A unique 3D to 3D matching study of 202 cadaveric femurs has demonstrated a significant difference in the average comparable shapes of male versus female distal femoral anatomy. For the same AP dimension, female distal femurs are more than 5mm narrower. Also the angle formed between the anterior condyles and the posterior condyles are significantly different with the female being more trapezoidal in shape.

Most existing total knee femoral component designs follow the ratio similar to that found in the average male distal femur. Options for management of this gender variability have been either utilizing instrumentation that references the anterior cortex to avoid notching or placing additional flexion on the distal femoral cut to allow downsizing. Both techniques are potentially problematic. Total knee implants systems are now utilizing this anthropomorphic data to redesign for separate male and female femoral components taking into consideration the relatively narrower female distal condylar width, lower medial anterior femoral condyle, and greater patellofemoral Q-angle.

Minimally invasive arthroplasty surgery has the potential advantage of accelerating recovery. The short-term advantages should not compromise the excellent long-term results that can be obtained with total knee replacement surgery via traditional surgical technique.

A study was performed to ascertain that MIS TKR was safe, especially in one’s early experience. The first 50 MIS surgeries performed by the author via a subv-astus surgical approach through a shorter incision were compared to a matched set of total knees performed with a standard rectus femoris splitting approach with a standard skin incision. No changes were made in anesthesia or rehabilitation protocols to determine the difference as result of the change in surgical technique only. The femoral and tibial bone cuts were performed in a conventional fashion from the front with specially designed smaller instruments. The average skin incision was 12cm in the MIS group and 21cm in the non-MIS group.The average tourniquet time wa 9 minutes longer in the MIS group, but the total surgery time was the same due to a shorter time for wound closure. Range of motion was the same. Pain levels were slightly less for the MIS group for the first 3 days. Rehabilitation was faster for the MIS group in terms of distance walking and advancement to a cane. There were no wound complications, infections or component malposition problems in either group.

MIS total knee replacement appears to be no worse than conventional total knee replacement through a muscle splitting wide skin exposure. The potential short-term advantage of faster rehabilitation and slightly less pain makes it an attactive technique for many total knee patients.