Background: Correct ligament balance is a critical factor in both cruciate retaining and substituting total knee arthroplasty (TKA). Due to a lack in current tools, however, little data exists on gap kinematics with the patella is in its anatomical position and with the ligaments tensed. The objective of this study was to quantify the effects of the patellar position and PCL resection on gap kinematics when constant tension is applied to the medial and lateral compartments.

Methods: A novel computer-controlled tensioner was used to measure the medial and lateral gaps in 10 normal knee specimens throughout a full range of motion. Gaps were measured medially and laterally using constant applied forces of 50N, 75N and 100N per side. Gap data were acquired at 0°, 30°, 60°, 90°, 120° of flexion. The test was performed with the patella everted and reduced, and with the PCL intact and resected.

Results: At 90° of flexion:

the mean medial gap was 1.5–2.5mm smaller than the mean lateral gap for all scenarios and forces tested (p< 0.05);

During knee flexion from 30° to 90°, the PCL tended to squeeze the medial compartment by 1–2mm (p< 0.05). Increasing the force from 50N to 100N per side resulted in a mean gap increase of 0.5mm throughout the range of flexion.

Conclusions: Measurement of gap kinematics with a computer-controlled tensioner and a completely reduced patella is feasible. Everting the patella and resecting the PCL both have significant effects on flexion gap balance and symmetry. Knees which are balanced with the patella everted may be post-operatively 1–3mm more lax in flexion than planned. Retaining the PCL may result in asymmetric tightening of the medial gap from 30° to 90°.

Background: Acquired patella baja occurs after both trauma and surgery of the knee including TKA, with prevalences between 30%–60%. The inferior position of the patella leads to alterations in the joint mechanics, reduction of range of motion, anterior knee pain, and can cause increased wear of the tibial and patellar polyethylene. Our aim was to evaluate the prevalence of patella baja after TKA and to assess the clinical effects of patella tendon torsion and twisting during surgical exposure of the knee.

Methods: Postoperative changes in patella height were measured on serial radiographs of 74 TKA implanted without patella eversion (group 1) and 57 TKA implanted with patella eversion (group 2). Pre- and postoperative Knee Society Scores, operative data, and complications were compared.

Results: With a cut-off level of 5% shortening, the prevalence was 12% (9 cases) in group 1 and 37% (21 cases) in group 2 (p=0.001). With the 10% cut-off level the prevalences were 5% (4 cases/group 1) and 14% (8 cases/group2) (p=0.1). The presence of patella baja was related to reduced flexion and increased pain 1 year after TKA.

Conclusion: Our study has shown that tension and twisting of the patellar tendon leads to shortening which was associated with reduced flexion and increased pain after TKA. By avoiding patella eversion the prevalence of acquired patella baja was reduced significantly.

Background: Recently, less invasive techniques for total knee arthroplasty (TKA) were introduced and the early results suggest a more rapid return of flexion and functional activities, while requiring fewer analgesics after surgery. Despite these findings, there is concern over the possibility of a steep learning curve and the potential risks of implant misalignment or poor fixation that may compromise long-term results. The purpose of this study was to analyze the potential learning curve effect on clinical and radiographic Results: Methods: This retrospective review compares the first 30 (Group 1) to the latest 30 cases (Group 2) in one surgeon’s consecutive series of 152 mini-incision mid-vastus TKA. Pre- and postoperative Knee Society Scores were compared, implant alignment was measured, and flexion was evaluated during hospital stay, at 6 weeks and 3 months after surgery. Complications and operative data were collected.

Results: Flexion was significantly higher in group 2 during hospitalization and at all clinical follow-up evaluations. At last follow-up mean flexion was 111° ± 8 (95–125) in group 1 and 121° ± 11 (90–140) in group 2 (p= 0.001). The mean length of skin incision was 11.7 cm ± 1.5 (8–15) with a mean incision length of the vastus medialis oblique muscle of 3.2 cm ± 1.0 (1–5). A steady improvement of knee and function scores was found in the entire series which were significantly greater in group 2. There were no complications and the radiographic evaluation found no implant or limb misalignment, or signs of early loosening.

Conclusion: The introduction of a mini-incision technique is an evolutionary process. The clinical and functional results show continued improvement after more than 100 cases. There was no classical learning curve effect and no increased complication rate in the earlier series. Thus far, the benefits of the mini-incision mid-vastus approach outweigh the new technique related difficulties and possible new risks. There are no signs of compromise that will affect the long-term results of mini-incision TKA.

Instruments are crucial to performing a knee replacement however they must be used properly.

Cutting guides may be solid blocks or slotted blocks. For the former the blade must be held on the surface of the block. A surgical peanut pressing the blade against the block helps. Slotted guides obviate this problem however the saw blade should be chosen so as not to bind in the slot, nor to be so thin that the blade wobbles in the slot. The most difficult resection is the posterior femoral resection. Because of the problem of holding a saw blade up against a cutting block, a slotted guide is best in this area. The cut should be checked twice since the hard bone in the posterior femoral condyles may cause the blade to deviate and result in an under-resection.

When blocks or guides are pinned to bone they should be inserted first through the convex side of the deformity (on the lateral side of a varus knee for instance). Often the bone on the concave side of a deformity is sclerotic and the pin may deviate changing the position of the block. A headed pin on the convex side will stabilise the block so that this will not occur.

Intramedullary femoral alignment rods should extend up to and slightly through the isthmus. The entrance point is NOT in the midline but slightly medial to this (it should be templated on the preoperative x-rays). Extramedullary guides for hip must be referenced from the femoral head; normal clinical evaluation for this is inaccurate and preoperative radiographic evaluation is usually necessary.

Intramedullary tibial alignment rods should enter at a point slightly anterior and medial to the midpoint of the tibia and should extend down to the level of the old distal tibial epiphyseal plate. The preoperative x-ray should be evaluated to ascertain the diameter of the canal. In some patients with a small intramedullary diameter a thinner rod may be necessary.

An extramedullary tibial alignment guide should be centred slightly medial to the mid malleolar point distally. In the lateral plane the reference landmark is the fibular shaft. A rod parallel to the fibular shaft will also be parallel to the midaxis of the tibia.

When any intramedullary guide is used the canal must be aspirated and washed to minimise the potential of fat embolisation. The rod should be fluted, the entrance hole large, and the insertion rate slow so as to avoid pressurisation of the medullary contents.

Preoperative templating essential