Does Anteromedial Portal Drilling Improve Footprint Placement in Anterior Cruciate Ligament Reconstruction?

BACKGROUND: Considerable debate remains over which anterior cruciate ligament (ACL) reconstruction technique can best restore knee stability. Traditionally, femoral tunnel drilling has been done through a previously drilled tibial tunnel; however, potential nonanatomic tunnel placement can produce a vertical graft, which although it would restore sagittal stability, it would not control rotational stability. To address this, some suggest that the femoral tunnel be created independently of the tibial tunnel through the use of an anteromedial (AM) portal, but whether this results in a more anatomic footprint or in stability comparable to that of the intact contralateral knee still remains controversial. QUESTIONS/PURPOSES: (1) Does the AM technique achieve footprints closer to anatomic than the transtibial (TT) technique? (2) Does the AM technique result in stability equivalent to that of the intact contralateral knee? (3) Are there differences in patient-reported outcomes between the two techniques? METHODS: Twenty male patients who underwent a bone-patellar tendon-bone autograft were recruited for this study, 10 in the TT group and 10 in the AM group. Patients in each group were randomly selected from four surgeons at our institution with both groups demonstrating similar demographics. The type of procedure chosen for each patient was based on the preferred technique of the surgeon. Some surgeons exclusively used the TT technique, whereas other surgeons specifically used the AM technique. Surgeons had no input on which patients were chosen to participate in this study. Mean postoperative time was 13 ± 2.8 and 15 ± 3.2 months for the TT and AM groups, respectively. Patients were identified retrospectively as having either the TT or AM Technique from our institutional database. At followup, clinical outcome scores were gathered as well as the footprint placement and knee stability assessed. To assess the footprint placement and knee stability, three-dimensional surface models of the femur, tibia, and ACL were created from MRI scans. The femoral and tibial footprints of the ACL reconstruction as compared with the intact contralateral ACL were determined. In addition, the AP displacement and rotational displacement of the femur were determined. Lastly, as a secondary measurement of stability, KT-1000 measurements were obtained at the followup visit. An a priori sample size calculation indicated that with 2n = 20 patients, we could detect a difference of 1 mm with 80% power at p < 0.05. A Welch two-sample t-test (p < 0.05) was performed to determine differences in the footprint measurements, AP displacement, rotational displacement, and KT-1000 measurements between the TT and AM groups. We further used the confidence interval approach with 90% confidence intervals on the pairwise mean group differences using a Games-Howell post hoc test to assess equivalence between the TT and AM groups for the previously mentioned measures. RESULTS: The AM and TT techniques were the same in terms of footprint except in the distal-proximal location of the femur. The TT for the femoral footprint (DP%D) was 9% ± 6%, whereas the AM was -1% ± 13% (p = 0.04). The TT technique resulted in a more proximal footprint and therefore a more vertical graft compared with intact ACL. The AP displacement and rotation between groups were the same and clinical outcomes did not demonstrate a difference. CONCLUSIONS: Although the AM portal drilling may place the femoral footprint in a more anatomic position, clinical stability and outcomes may be similar as long as attempts are made at creating an anatomic position of the graft. LEVEL OF EVIDENCE: Level III, therapeutic study.

Retrospective analysis of total knee arthroplasty cases for visual, histological, and clinical eligibility of unicompartmental knee arthroplasties.

We retrospectively analyzed 97 total knee arthroplasty cases with medial osteoarthritis from seven participating surgeons in our teaching hospital to determine the percentage of patients who met the following eligibility criteria for unicompartmental knee arthroplasty (UKA): healthy cartilage in the lateral compartment based on (1) visual analysis, (2) histological analysis and (3) absence of UKA contraindications based on clinical analysis. The cases with healthy lateral cartilage, intact anterior cruciate ligament and posterior cruciate ligament, lack of patello-femoral arthritis, preoperative range of motion (ROM) greater than 90, and genu varum less than 10° represented 21% of the 97 cases studied. This percentage would likely have been higher had the cases been assessed earlier in the disease process. It was concluded that there is the potential to utilize UKA more frequently in the future.

Contact Analysis of Horizontal Cleavage Tear Treatment.

Horizontal cleavage tears (HCT) commonly occur in the posterior horn of the medial meniscus due to aging and degeneration. The purpose of this study was to investigate the surgical treatment of HCTs and their effect on dynamic tibiofemoral contact mechanics. The tibiofemoral contact mechanics of 10 cadaver knees were investigated using a custom dynamic loading apparatus, pressure sensor, and motion sensing camera. Three loading conditions were analyzed: 500 N compressive load, 500 N compressive load with 100 N posterior shear, and 500 N compressive load with 2.5 Nm of internal torque. Real-time peak contact pressures and contact areas were recorded throughout the full range of motion. After testing the intact meniscal state, a horizontal cleavage tear was created and included 50% of the width of the meniscus. The following procedures were performed, and the loading conditions described above were analyzed: HCT superior flap removal (5 specimens), HCT inferior flap removal (remaining 5 specimens), and both flaps removed (all 10 specimens). Statistical analysis was performed using a mixed linear effects model using the R-statistical package. The mixed linear effects statistical model identified statistically significant differences between independent variables, including the procedure performed, meniscal flap removed, meniscal region, loading condition, and knee flexion angle with respect to contact area and peak contact pressure. Peak contact pressure and contact area were not affected by selective flap removal (superior vs. inferior) or removal of both flaps of the HCT. We recommend that in the treatment of horizontal cleavage tears of the posterior horn of the medial meniscus, the outer 50% of the posterior horn of the medial meniscus should be maintained for load transmission.

Relationship between meniscal integrity and risk factors for cartilage degeneration.

BACKGROUND: The purpose of this study was to use MRI to determine if a loss of meniscal intra-substance integrity, as determined by T2* relaxation time, is associated with an increase of Kellgren-Lawrence (KL) grade, and if this was correlated with risk factors for cartilage degeneration, namely meniscal extrusion, contact area and anterior-posterior (AP) displacement. METHODS: Eleven symptomatic knees with a KL 2 to 4 and 11 control knees with a KL 0 to 1 were studied. A 3 Tesla MRI scanner was used to scan all knees at 15° of flexion. With a 222N compression applied, a 3D SPACE sequence was obtained, followed by a spin echo 3D T2* mapping sequence. Next, an internal tibial torque of 5Nm was added and a second 3D SPACE sequence obtained. The MRI scans were post-processed to evaluate meniscal extrusion, contact area, AP displacement and T2* relaxation time. RESULTS: KL grade was correlated with T2* relaxation time for both the anterior medial meniscus (r=0.79, p<0.001) and the posterior lateral meniscus (r=0.55, p=0.009). In addition, T2* relaxation time was found to be correlated with risk factors for cartilage degeneration. The largest increases in meniscal extrusion and decreases in contact area were noted for those with meniscal tears (KL 3 to 4). All patients with KL 3 to 4 indicated evidence of meniscal tears. CONCLUSIONS: This suggests that a loss of meniscal integrity, in the form of intra-substance degeneration, is correlated with risk factors for cartilage degeneration.

Characterising knee motion and laxity in a testing machine for application to total knee evaluation.

The goal of this study was to determine knee motions in specimens under combined input forces over a full range of flexion, so that the various flexion angles and loading combinations encountered in functional conditions would be contained. The purpose was that the data would act as a benchmark for the evaluation of TKR designs using the same testing methodology. We measured the neutral path of motion and laxity about the neutral path. The femur was flexed in a continuous movement, rather than at discrete flexion angles, using optical tracking. The motion of the femoral circular axis relative to the tibia was determined, as well as the contact patches on the tibial surfaces. The neutral path of motion was independent of compressive load, and consisted of a relatively constant medial contact and steady posterior displacement laterally, in agreement with previous studies. The anterior-posterior laxities of the lateral and medial condyles were similar whether AP forces or torques were applied. The lateral laxity was predominantly anterior with respect to the neutral path, while on the medial side, the laxity was less than lateral and predominantly posterior of the neutral path. Contact on the anterior surface of the medial tibial plateau only occurred in some cases in 5° hyperextension and at 0° flex when an anterior femoral shear or an external femoral torque were applied. The method can be regarded as a development of the ASTM constraint standard, with the addition of the benchmark, for the evaluation of total knee designs.

Function of the medial meniscus in force transmission and stability.

We studied the combined role of the medial meniscus in distributing load and providing stability. Ten normal knees were loaded in combinations of compressive and shear loading as the knee was flexed over a full range. A digital camera tracked the motion, from which femoral-tibial contacts were determined by computer modelling. Load transmission was determined from the Tekscan for the anterior horn, central body, posterior horn, and the uncovered cartilage in the centre of the meniscus. For the three types of loading; compression only, compression and anterior shear, compression and posterior shear; between 40% and 80% of the total load was transmitted through the meniscus. The overall average was 58%, the remaining 42% being transmitted through the uncovered cartilage. The anterior horn was loaded only up to 30 degrees flexion, but played a role in controlling anterior femoral displacement. The central body was loaded 10-20% which would provide some restraint to medial femoral subluxation. Overall the posterior horn carried the highest percentage of the shear load, especially after 30 degrees flexion when a posterior shear force was applied, where the meniscus was estimated to carry 50% of the shear force. This study added new insights into meniscal function during weight bearing conditions, particularly its role in early flexion, and in transmitting shear forces.

Tibiofemoral contact mechanics following a horizontal cleavage lesion in the posterior horn of the medial meniscus.

The purpose of this study was to determine if a horizontal cleavage lesion (HCL) of the posterior horn of the medial meniscus would result in changes to tibiofemoral contact mechanics, as measured by peak contact pressure and contact area, which can lead to cartilage degeneration. To study this, 10 cadaveric knees were tested in a rig where forces were applied (500 N Compression, 100 N shear, 2.5 Nm Torque) and the knee dynamically flexed from -5° to 135°, as peak contact pressure and contact area were recorded. After testing of the intact knee, a horizontal cleavage lesion was created arthroscopically and testing repeated. The Wilcoxon signed-rank test was used to determine if there were differences in peak contact pressure and contact area between the intact knee and that with the HCL. A statistically significant increase in peak contact pressure of 13%, on average, and a decrease in contact area of 6%, on average, was noted following the HCL. This suggests that a horizontal cleavage lesion will result in small but statistically significant changes in tibiofemoral contact mechanics which may lead to cartilage degeneration.

The effect of arthroscopic partial medial meniscectomy on tibiofemoral stability.

BACKGROUND: There is still little known regarding the effects of meniscus resection size on tibiofemoral stability. PURPOSE: To determine if partial medial meniscectomy of the posterior horn significantly alters tibiofemoral stability as measured by the anterior-posterior (AP) position and laxity of the medial femoral condyle. STUDY DESIGN: Controlled laboratory study. METHODS: Five cadaveric knees were dissected to the capsule, preserving all ligaments and the quadriceps tendon. Each specimen was first tested on a rig where the AP position and laxity of the medial femoral condyle were measured while a range of forces was applied from full extension to 90° of flexion. Magnetic resonance imaging (MRI) at 3 tesla was then performed for baseline measurements of the meniscus before partial meniscectomy. Arthroscopic partial medial meniscectomy aimed at 30% of the posterior horn was then performed, followed by repeat mechanical testing and MRI. The sequence was then repeated for arthroscopic partial meniscectomy aimed at 60% and 100% of the posterior horn of the medial meniscus. RESULTS: The MRI analysis demonstrated that 22% ± 9% of the original width of the posterior horn was removed at the first resection, 46% ± 11% was removed at the second resection, and the third resection was 100% removal of the posterior horn for all specimens. After 22% resection, no significant difference in AP laxity was observed. A statistically significant increase in AP laxity was observed with 46% resection under a 500-N compressive load compared with the intact meniscus. After full resection, significant increases in AP laxity were observed under a 50-N compressive load compared with the intact and 22% and 46% resections. The 22% resection had similar AP positions as the intact knee, whereas the 46% resection and 100% removal of the posterior horn had statistically further posterior AP positions than the intact knee. CONCLUSION: Partial medial meniscectomy with ≥46% resection of the original width of the posterior horn significantly altered the AP position of the medial femoral condyle and also increased laxity. CLINICAL RELEVANCE: These mechanical changes may lead to abnormal cartilage loading and early osteoarthritis.

Anterior-posterior stability of the knee by an MR image subtraction method.

The purpose of our study was to test the hypothesis that when a shear force was applied posteriorly to the loaded knee in vivo, there would be no relative motion between the tibia and the medial femoral condyle. Siemens 7 Tesla high-resolution MRI machine was used to scan eight healthy male volunteers with the knee at 15° of flexion. Two scans were obtained: the first with a compressive force of 660 N along the tibial long axis and a second with the compressive force and a posterior shear force of 36 N applied to the tibia. Solid models were created of the femur, tibia, and menisci for both loading conditions. The tibial models were superimposed enabling the displacements of the femur and menisci to be determined, relative to a fixed tibia. On average, the lateral femoral condyle displaced anteriorly by 0.66 mm but the medial femoral condyle displaced posteriorly by 0.36 mm. This indicated an axial rotation with a center between the lateral and medial condyles, but closer to the medial. The menisci displaced with the femoral condyles, but there was no indication that the medial meniscus was contributing to the pivoting action. This study supported the concept of medial anterior-posterior stability under weight-bearing conditions, but with structures other than the medial meniscus providing the stability. This study has application to the treatment of knee injuries and to knee arthroplasty design.

Relation between cartilage volume and meniscal contact in medial osteoarthritis of the knee.

BACKGROUND: The purpose was to determine the relationship between the cartilage volumes in different regions of the femur and tibia, and the lengths of contacts between the meniscus and cartilage. The rationale was that less meniscal contact would make the cartilage more susceptible to loss of volume due to degeneration and wear. METHODS: Fifty MRI scans of osteoarthritic knees at varying degrees of severity were obtained. Computer models of the cartilage layers of the distal femur and proximal tibia were generated, from which cartilage volumes and thicknesses were calculated for different regions. The lengths of meniscal contact and heights were measured in frontal and sagittal views. RESULTS: Cartilage loss progressed initially on the central and inner regions of the distal femur, and on the tibia in the region uncovered by the meniscus. As the cartilage volume decreased further, the wear spread medially, and to a lesser extent anteriorly and posteriorly. There were inverse relations between the loss of volume on both the femur and tibia, and the meniscal contacts and heights. CONCLUSIONS: Cartilage loss initially occurred where there was direct contact between the cartilage of the femur and tibia. The meniscus did not prevent this, nor prevent the spread of the wear medially. This may have been due to the progressive reduction of cartilage-meniscal contact as the meniscus subluxed or lost substance, as the cartilage loss and deformity progressed. This suggested that the meniscus was not able to ameliorate the forces and pressures on the cartilage surfaces to prevent degeneration.

Evaluation of femoral strains with cementless proximal-fill femoral implants of varied stem length.

BACKGROUND: The design intent of proximally-filling lateral flare femoral stems is to load the endosteal surface of the proximal femur both laterally and medially, to achieve normal bone strains. However, the long stem can contact the femoral cortex and may offload the proximal region to some extent. Therefore, in this study, we sought to determine if reducing the stem length, would result in physiologic strain patterns. METHODS: Using the PhotoStress® method we analyzed 13 femurs intact and with three different stem length implants: stemless, ultra-short and short. The test rig loaded the femoral head by simulating the mid-stance single leg support phase of gait with the ilio-tibial band and the hip abductor forces. The strain distribution with each stem length implant was then compared to the intact strain distribution to determine which was most similar. FINDINGS: As the stem length increased the femurs exhibited a typical pattern of reduced proximal strain and increased distal strain. However, there was some variation in this pattern indicating that the exact stem position and the location of its interaction with the endosteal surface of bone was not the same in each femur. INTERPRETATION: The stemless design provided the best match compared to the native femur and therefore has the greatest potential to address the shortcomings of a stemmed femoral implant. However, the ultra-short implant also exhibited a strain distribution that closely emulated the intact femur, and may represent the best option as there are still several questions pertaining to stability and alignment of a stemless implant.