Anthony M. J. Bull

A Biomechanical Comparison of Single and Double-Row Fixation in Arthroscopic Rotator Cuff Repair

BACKGROUND The optimal method for arthroscopic rotator cuff repair is not yet known. The hypothesis of the present study was that a double-row repair would demonstrate superior static and cyclic mechanical behavior when compared with a single-row repair. The specific aims were to measure gap formation at the bone-tendon interface under static creep loading and the ultimate strength and mode of failure of both methods of repair under cyclic loading. METHODS A standardized tear of the supraspinatus tendon was created in sixteen fresh cadaveric shoulders. Arthroscopic rotator cuff repairs were performed with use of either a double-row technique (eight specimens) or a single-row technique (eight specimens) with nonabsorbable sutures that were double-loaded on a titanium suture anchor. The repairs were loaded statically for one hour, and the gap formation was measured. Cyclic loading to failure was then performed. RESULTS Gap formation during static loading was significantly greater in the single-row group than in the double-row group (mean and standard deviation, 5.0 +/- 1.2 mm compared with 3.8 +/- 1.4 mm; p < 0.05). Under cyclic loading, the double-row repairs failed at a mean of 320 +/- 96.9 N whereas the single-row repairs failed at a mean of 224 +/- 147.9 N (p = 0.058). Three single-row repairs and three double-row repairs failed as a result of suture cut-through. Four single-row repairs and one double-row repair failed as a result of anchor or suture failure. The remaining five repairs did not fail, and a midsubstance tear of the tendon occurred. CONCLUSIONS Although more technically demanding, the double-row technique demonstrates superior resistance to gap formation under static loading as compared with the single-row technique. CLINICAL RELEVANCE A double-row reconstruction of the supraspinatus tendon insertion may provide a more reliable construct than a single-row repair and could be used as an alternative to open reconstruction for the treatment of isolated tears.

Technologies for global health

Institute for Global Health Innovation (L Conteh PhD, Prof A Darzi FRCS, P Howitt MA, K Kerr PhD, Prof S Matlin DSc, R Merrifi eld PhD, Prof G-Z Yang PhD), Centre for Environmental Policy (E Wilson MSc), Centre for Health Policy (D King MRCS, M Kulendran MRCS, Prof P C Smith BA), Department of Bioengineering (Prof A M J Bull PhD, Prof R A Malkin PhD, Prof M M Stevens PhD), Department of Civil and Environmental Engineering (M R Templeton PhD), Department of Infectious Diseases (G S Cooke PhD, N Ford PhD, S D Reid PhD), Department of Infectious Disease Epidemiology (S A J Gregson PhD), Department of Materials (Prof M M Stevens), Department of Medicine (A Blakemore PhD), Department of Primary Care & Public Health (Prof A Majeed MD), Department of Surgery and Cancer (H Ashrafi an MRCS, Prof C Vincent PhD), Faculty of Medicine (Prof R Atun FRCP), Global eHealth Unit (J Car PhD), Imperial College Business School (Prof R Atun FRCP, Prof J Barlow PhD), and Imperial Innovations (HA Penfold PhD), Imperial College London, London, UK Technologies for global health

Intraoperative measurement of knee kinematics in reconstruction of the anterior cruciate ligament

Our objectives were to establish the envelope of passive movement and to demonstrate the kinematic behaviour of the knee during standard clinical tests before and after reconstruction of the anterior cruciate ligament (ACL). An electromagnetic device was used to measure movement of the joint during surgery. Reconstruction of the ACL significantly reduced the overall envelope of tibial rotation (10 degrees to 90 degrees flexion), moved this envelope into external rotation from 0 degrees to 20 degrees flexion, and reduced the anterior position of the tibial plateau (5 degrees to 30 degrees flexion) (p < 0.05 for all). During the pivot-shift test in early flexion there was progressive anterior tibial subluxation with internal rotation. These subluxations reversed suddenly around a mean position of 36 +/- 9 degrees of flexion of the knee and consisted of an external tibial rotation of 13 +/- 8 degrees combined with a posterior tibial translation of 12 +/- 8 mm. This abnormal movement was abolished after reconstruction of the ACL.

The Role of the Medial Collateral Ligament and Posteromedial Capsule in Controlling Knee Laxity

Background The medial aspect of the knee has a complex capsular structure; the biomechanical roles of specific structures are not well understood. Hypothesis The 3 strong stabilizing structures, the superficial and deep medial collateral ligaments and the posteromedial capsule, make distinct contributions to controlling tibiofemoral laxity. Study Design Controlled laboratory study. Methods Changes in knee laxity under anterior-posterior drawer, valgus, and internal-external rotation loads were found by sequential cutting in 18 cadaveric knees. Three cutting sequences allowed the roles of the 3 structures to be seen in isolation and in combination. Some force contributions were also calculated. Results The posteromedial capsule controlled valgus, internal rotation, and posterior drawer in extension, resisting 42% of a 150-N drawer force when the tibia was in internal rotation. The superficial collateral ligament controlled valgus at all angles and was dominant from 30° to 90° of flexion, plus internal rotation in flexion. The deep collateral ligament controlled tibial anterior drawer of the flexed and externally rotated knee and was a secondary restraint to valgus. Conclusion Distinct roles in controlling tibiofemoral laxity have been found for these structures that vary according to knee flexion and tibial rotation. Clinical Relevance The restraining functions demonstrated provide new information about knee stabilization, which may allow better evaluation of structural damage at the medial aspect of the knee.

Measurement of patellar tracking: assessment and analysis of the literature.

Patellar tracking is defined as the motion of the patella relative to the femur or femoral groove on knee flexion and extension. Abnormalities of tracking (maltracking) are thought to relate to many disorders of the patellofemoral joint and may be defined easily or may be extremely difficult to observe. Accurate measurement of patellar tracking, and definition of normal tracking, have not been achieved yet in experimental conditions or in clinical conditions. Such information would be valuable in the diagnosis and treatment of patellofemoral disorders. In the current report, the literature is reviewed critically with an emphasis on methodology and results. The reporting of patellar tracking is affected significantly by basic definitions of coordinate systems and reference points. The method of muscle loading, range, and direction of knee motion, use of static or dynamic measurement techniques, and tibial rotation also will affect the results obtained. The accuracy of the equipment used is important as differences in tracking may be small. Comparison between existing studies is difficult because of differences in methodology. There is general agreement that the patella translates medially in early knee flexion and then translates laterally. Regarding patellar tilt, results are less consistent, especially in vivo and the results for patellar rotation are highly variable.

Femoral attachment of the anterior cruciate ligament

Endoscopic anterior cruciate ligament (ACL) reconstruction is one of the most popular orthopaedic procedures. Correct tunnel positioning is a prerequisite to success. Current surgical techniques are unable to duplicate the complex anatomy and function of the native ACL. Surgery mainly aims at restoring anteroposterior laxity. The ACL is not isometric and only a few fibers are nearly isometric over the full range of motion. However, a nearly isometric behaviour of the ACL graft is desirable. Isometry is mainly influenced by femoral attachment; thus the femoral tunnel position has a greater effect than the tibial on graft length changes. The purpose of this article is to describe the anatomy of the femoral ACL insertion and to discuss the surgical techniques used to replicate it.

Quantitative measurement of patellofemoral joint stability: force–displacement behavior of the human patella in vitro ☆

Patellofemoral joint instability is a common clinical problem. However, little quantitative data are available describing the stability characteristics of this joint. We measured the stability of the patella against both lateral and medial displacements across a range of knee flexion angles while the quadriceps were loaded physiologically. For eight fresh‐frozen knee specimens a materials testing machine was used to displace the patella 10 mm laterally and 10 mm medially while measuring the required force, with 175 N quadriceps tension. The patella was connected via a ball‐bearing patellar mounting 10 mm deep to the anterior surface to allow natural tilt and other rotations. Patellar force–displacement behavior was tested at flexion angles of 0°, 10°, 20°, 30°, 45°, 60°, and 90°. Significant differences were found between the lateral and medial restraining forces at 10 mm displacement. For lateral displacement, the restraining force was least at 20° of knee flexion (74 N at 10 mm displacement), rising to 125 N at 0° and 90° of knee flexion. The restraining force increased progressively with knee flexion for medial patellar displacement, from 147 N at 0° to 238 N at 90°. With quadriceps tension, the patella was more resistant to medial than lateral displacement. Our finding that lateral patellar displacement occurred at the lowest restraining force when the knee was flexed 20° agrees with clinical experience of patellar instability.

The pivot-shift phenomenon: a clinical and biomechanical perspective

Abstract The current literature on the assessment, treatment and effect of the pivot shift is reviewed. Various questions pertaining to the cause of the pivot shift, the three-dimensional dynamic kinematics and the specific procedures required to reconstruct a knee that demonstrates the pivot shift are found to be unanswered. Biomechanical studies are presented, but it is unlikely that any research will be able to refute or reconcile all of the conflicting statements published in the literature, because of the notable differences in geometry, anatomy and soft tissue properties between different knees. However, there is scope for clarifying and explaining these results.

The cartilaginous and osseous geometry of the femoral trochlear groove

Photography was used to study the geometry of the cartilaginous and osseous contours of the distal femur and the orientation of the trochlear groove in 9 fresh-frozen and 24 embalmed knees. The sulcus angle (146.1°±5.5°) decreased from 0° to 50° of femoral flexion then increased afterwards. The maximum slope of the lateral femoral condyle (20.2°±5.2°) also decreased with flexion. Both the sulcus angle (p =0.0007) and maximum slope (p =0.0001) were larger at 0° than they were for 60° cartilaginous surfaces. The lateral femoral condylar height decreased, whilst the medial femoral condylar height increased as the flexion increased. The femoral groove was midway between the two femoral epicondyles (49.5±3.9%), but deviated laterally as the flexion angle increased. The groove axis deviated distally and laterally from the femoral anatomical axis for both cartilaginous and bony surfaces, and the angle between the groove and anatomical axes was similar for both cartilaginous (19.1°) and osseous (16.8°) surfaces. Articular cartilage is not well represented on radiography yet it had a significant effect on the distal femoral geometry, and should be taken into account when evaluating the patellofemoral joint.

The effect of trochleoplasty on patellar stability and kinematics: A BIOMECHANICAL STUDY IN VITRO

Objective patellar instability has been correlated with dysplasia of the femoral trochlea. This in vitro study tested the hypothesis that trochleoplasty would increase patellar stability and normalise the kinematics of a knee with a dysplastic trochlea. Six fresh-frozen knees were loaded via the heads of the quadriceps. The patella was displaced 10 mm laterally and the displacing force was measured from 0 degrees to 90 degrees of flexion. Patellar tracking was measured from 0 degrees to 130 degrees of knee flexion using magnetic sensors. These tests were repeated after raising the central anterior trochlea to simulate dysplasia, and repeated again after performing a trochleoplasty on each specimen. The simulated dysplasia significantly reduced stability from that of the normal knee (p < 0.001). Trochleoplasty significantly increased the stability (p < 0.001), so that it did not then differ significantly from the normal knee (p = 0.244). There were small but statistically significant changes in patellar tracking (p< 0.001). This study has provided objective biomechanical data to support the use of trochleoplasty in the treatment of patellar instability associated with femoral trochlear dysplasia.