Patrick Meere

Effects of surgical variables in balancing of total knee replacements using an instrumented tibial trial

BACKGROUND In total knee surgery, typically the bone cuts are made first to produce the correct overall alignment. This is followed by balancing, often using spacer blocks to obtain equal parallel gaps in flexion and extension. Recently an electronically instrumented tibial trial has been introduced, which measures lateral and medial contact forces. The goal of our study was to determine the effect of different surgical variables; changing component sizes, modifying bone cuts, or ligament releases; on the contact forces, as a method to achieve balancing. METHODS A special rig was designed to fit on a standard operating table, on which tests on 10 lower extremity specimens were carried out. After making bone cuts for a posterior cruciate retaining knee using a navigation system, tibial thickness was determined in extension using the Sag Test. Different Surgical Variables were then implemented, and the changes in the condylar forces were determined throughout flexion using the Heel Push Test. RESULTS condylar forces were found to consist of gravity forces due to the weight of the leg plus forces due to pretension in the collateral ligaments. The pretension force averaged 145 N but there was considerable variation because of ligament stiffness properties. Balancing from an imbalanced state could be achieved with adjustments within only 2° or 2 mm. CONCLUSION The instrumented tibial trial provided force information which indicated which surgical correction options to carry out to achieve balancing. From an initial unbalanced state, relatively small changes could produce balancing, indicating the sensitivity of the procedure. CLINICAL RELEVANCE Non-clinical. This study will assist in the balancing of the knee at total knee replacement surgery.

Effect of a Perioperative Intra-articular Injection on Pain Control and Early Range of Motion Following Bilateral TKA

Pain control after total knee arthroplasty (TKA) is integral in the immediate postoperative period for early rehabilitation. Numerous different methods of postoperative analgesia are available, but each has its own risk of adverse side effects. This study was performed to prospectively evaluate the benefits of an intra-articular analgesic injection in patients undergoing bilateral TKA.Thirty consecutive patients undergoing bilateral TKA were enrolled in this prospective, randomized, controlled study. Each patient was randomized to receive (1) a perioperative intra-articular mixture of morphine, bupivacaine with epinephrine, and ketorolac in 1 knee, and (2) injectable sterile saline in the contralateral knee. Each patient acted as his or her own internal control. The pharmacologically injected knee had statistically significantly less pain immediately postoperatively when compared to the control knee and displayed significantly increased range of motion within the first week of rehabilitation.The use of an intraoperative intra-articular injection with the above drug combination significantly reduces patient pain and increases postoperative mobility with no apparent risks following bilateral TKA.

Contact forces in the tibiofemoral joint from soft tissue tensions: Implications to soft tissue balancing in total knee arthroplasty

Proper tension of the knees soft tissue envelope is important during total knee arthroplasty; incorrect tensioning potentially leads to joint stiffness or instability. The latter remains an important trigger for revision surgery. The use of sensors quantifying the intra-articular loads, allows surgeons to assess the ligament tension at the time of surgery. However, realistic target values are missing. In the framework of this paper, eight non-arthritic cadaveric specimens were tested and the intra-articular loads transferred by the medial and lateral compartment were measured using custom sensor modules. These modules were inserted below the articulating surfaces of the proximal tibia, with the specimens mounted on a test setup that mimics surgical conditions. For both compartments, the highest loads are observed in full extension. While creating knee flexion by lifting the femur and flexing the hip, mean values (standard deviation) of 114N (71N) and 63N (28N) are observed at 0° flexion for the medial and lateral compartment respectively. Upon flexion, both medial and lateral loads decrease with mean values at 90° flexion of 30N (22N) and 6N (5N) respectively. The majority of the load is transmitted through the medial compartment. These observations are linked to the deformation of the medial and lateral collaterals, in addition to the anatomy of the passive soft tissues surrounding the knee. In conclusion, these findings provide tangible clinical guidance in assessing the soft tissue loads when dealing with anatomically designed total knee implants.

Identification of the landmark registration safe zones during total knee arthroplasty using an imageless navigation system

Incorrect registration during computer assisted total knee arthroplasty (CA-TKA) leads to malposition of implants. Our aim was to evaluate the tolerable error in anatomic landmark registration. We incorrectly registered the femoral epicondyles, femoral and tibial centers, as well as the malleoli and documented the change in angulation or rotation. We found that the distal femoral epicondyles were the most difficult anatomic landmarks to register. The other bony landmarks were more forgiving. Identification of the distal femoral epicondyles has a high inter-observer and intra-observer variability. Our observation that there is less than 2mm of safe zone in the anterior or posterior direction during registration of the medial and lateral epicondyles may explain the inability of CA-TKA to improve upon the outcomes of conventional TKA.

Incidence of Patellar Clunk Syndrome in Fixed Versus High-Flex Mobile Bearing Posterior-Stabilized Total Knee Arthroplasty

The geometry of the intercondylar box plays a significant role in the development of patellar clunk syndrome. We reviewed the incidence of patella clunk at mid-to-long-term follow-up of a rotating high-flex versus fixed bearing posterior stabilized TKA design. 188-mobile and 223-fixed bearing TKAs were reviewed for complications, incidence of patellar clunk, treatment, recurrence rates, range of motion, and patient satisfaction. Patellar clunk developed in 22 knees in the mobile (11.7%) and in 4 (1.8%) in the fixed bearing group (P<0.001). 23 out of 26 cases resolved with a single arthroscopic treatment and 2 resolved with a second procedure. The mean postoperative range of motion was 122.4°. All but one patient reported overall satisfaction with the index procedure. In contrast with other recent studies we found a significant incidence of patellar clunk in high-flex mobile bearings. Despite the high rate of patellar clunk syndrome, overall patients did well and were satisfied with their outcomes.

Computer-assisted surgery patterns of ligamentous deformity of the knee: a clinical and cadaveric study.

Knee malalignment during total knee arthroplasty (TKA) is commonly classified as either varus or valgus on the basis of a standing anteroposterior radiograph. Computer-assisted surgery (CAS) navigation TKA provides precise dynamic evaluation of knee alignment throughout the full range of motion (FROM). The goal of this study was to classify patterns of CAS-generated knee deformity curves that match specific soft tissue contracture combinations. This can then be applied as an algorithm for soft tissue balancing on the basis of the preoperative knee deformity curve. Computer navigation-generated graphs from 65 consecutive TKA procedures performed by a single surgeon were analyzed. A stress-strain curve of the coronal alignment of the knee was recorded throughout FROM before bony resection. All graphs were classified into groups according to their pattern. Cadaveric knee models were then used to test the correlation between isolated and combined ligamentous contractures and identified CAS deformity curves. An analysis of the intraoperative knee alignment graphs revealed four distinct patterns of coronal deformity on the basis of intraoperative data: 13% diagonal, 18.5% C-shaped, 43.5% comma shaped, and 25% S-shaped. Each represents the change in varus and valgus alignment during FROM. All patterns were reproduced with cadaveric knees by recreating specific contracture constellations. A tight posterior capsule gave an S-shaped curve, a tight lateral collateral ligament gave a C-shaped curve, tight medial collateral ligament gave a diagonal curve, and a tight posterior lateral corner gave a comma-shaped curve. Release of the specific contractures resulted in correction of all patterns of deformity as measured by CAS. We propose a new classification system for coronal plane knee deformity throughout FROM. This system intends to match individual and combined soft tissue pathological contractures to specific stress-strain curves obtained through routine knee CAS preparation. This classification system may provide surgeons with a general guide for soft tissue balancing during computer-navigated TKA.

Navigation and Robotics in Knee Arthroplasty

Computer-assisted surgery for total knee arthroplasty can be performed with use of computer-assisted navigation, handheld navigation, partially or fully robot-assisted technology, and patient-specific instrumentation.Computer-assisted navigation leads to improved component alignment and a reduction

Laxity and contact forces of total knee designed for anatomic motion: A cadaveric study

BACKGROUND Total knee designs that attempt to reproduce more physiological knee kinematics are gaining attention given their possible improvement in functional outcomes. This study examined if a total knee designed for anatomic motion, where the soft tissue balancing was intended to replicate anatomical tibiofemoral contact forces, can more closely reproduce the laxity of the native knee. METHODS In an ex-vivo setting, the laxity envelope of the knees from nine lower extremity specimens was measured using a rig that reproduced surgical conditions. The rig allowed application of a constant varus/valgus (V/V) and internal-external (I/E) torque through the range of motion. After testing the native knee, total knee arthroplasty (TKA) was performed using the Journey II bi-cruciate substituting implant. Soft tissue balancing was guided by targeting anatomical compressive forces in the lateral and medial tibiofemoral joints with an instrumented tibial trial. After TKA surgery, the laxity tests were repeated and compared to the native condition. RESULTS The TKA knee closely reproduced the coronal laxity of the native knee, except for a difference at 90° of flexion for valgus laxity. Looking at the rotational laxity, the implant constrained the internal rotation relative to the native knee at 45 and 60° of flexion. The forces on the tibial trial for the neutral path of motion showed higher values on the medial side as the knee flexed. CONCLUSIONS This study suggested that when using an anatomically-designed knee, the soft tissue balancing should also aim for anatomical contact forces, which will result in close to normal laxity patterns.