Biomedical subjects

Michael Dienst

Publications and source records attributed to Michael Dienst.

12 recordsLinked to original sources

PubMed2006

Effect of lateral meniscal allograft sizing on contact mechanics of the lateral tibial plateau: an experimental study in human cadaveric knee joints.

BACKGROUND: A mismatch of the original lateral meniscus and a lateral meniscus allograft by inaccurate preoperative radiographic sizing can have significant consequences on ultimate function. HYPOTHESIS: The size of a lateral meniscal allograft affects the contact mechanics of the femoral condyle on the tibial plateau. STUDY DESIGN: Controlled laboratory study. METHODS: Four right and 2 left knees were tested as intact joints, after meniscectomy, and after replantation with the original menisci and 16 right or 9 left human, fresh-frozen lateral meniscal allografts, respectively. The allografts were allocated into 7 groups according to their outer and inner anteroposterior and mediolateral diameters. Biomechanical testing was performed as compressive loadings with constrained motions in extension and 30 degrees of flexion. Measurements were done with Fuji pressure-sensitive films for contact parameters of the direct femorotibial and meniscotibial contact. RESULTS: Oversized lateral meniscal allografts led to greater forces across the articular cartilage, whereas undersized allografts resulted in normal forces across the articular cartilage but greater forces across the meniscus. Two undersized transplants failed. Most of the contact parameters of allografts 10% smaller or larger than the original menisci were in the range of the intact knees. The knees after meniscectomy showed greater forces of the direct femorotibial contact areas than did the intact knees and the knees with the replanted original menisci. The contact mechanics of the knees with the replanted original menisci were close to normal. CONCLUSION: The size of a lateral meniscal allograft has a significant effect on the contact mechanics of the tibial plateau. CLINICAL RELEVANCE: Preoperative radiographic sizing needs to be performed precisely to identify a suitable lateral meniscal allograft. A mismatch may be the reason for failure of the allograft or subsequent development of degenerative changes. A mismatch on graft selection of less than 10% of the size of the original meniscus may be acceptable.

Aged↗

PubMed2006

Correlation of intercondylar notch cross sections to the ACL size: a high resolution MR tomographic in vivo analysis.

INTRODUCTION: To correlate cross sections of the intercondylar notch to cross sections of the anterior cruciate ligament (ACL) and to analyze gender-related differences in notch and ACL morphometry with an attempt to explain the observation that a small intercondylar notch and the female gender predispose to a rupture of the ACL. MATERIAL AND METHODS: High resolution MR imaging was performed on a 1.5 T magnet using a dedicated extremity-coil in ten left and ten right knee joints of 20 volunteers (10 male, 10 female, mean age 25 years) with no history of knee abnormalities. Continuous axial T2-weighted MR images perpendicular to the longitudinal axis of the ACL were acquired. Cross-sectional areas of the ACL midsubstance at the contact area to the posterior cruciate ligament were measured. For imaging and evaluation of the osseous limits of the intercondylar notch a 3D-dataset of the knee was acquired. Anterior, middle and posterior planes of the intercondylar notch were calculated and analyzed for measurement of the notch area AN and notch width index NWI. The ratio of the ACL cross-sectional area of the ACL and the cross-sectional area of the notch was defined as the ACL notch index (ANI) and used as a standardized tool for evaluation. For statistical evaluation, linear regression analysis was performed. Mean values between male and female were compared using a t test. In addition, five matched pairs of male and female volunteers of same height were analyzed. RESULTS: Mean cross-sectional size of the ACL at the crossing with the PCL was 54.4 +/- 20.4 mm2. Regression analysis showed a significant correlation (P < 0.05) of the ACL cross-sectional area to the notch areas on all three planes and NWI, respectively. Comparison between the sexes revealed that female participants had significantly smaller cross-sectional areas of the ACL, the notch areas, the NWI and ANI. This difference was found for both the complete study group and the matched pairs of same height. CONCLUSIONS: The smaller the intercondylar notch the smaller the cross-sectional area of the ACL midsubstance. In addition to the impingement of the ACL at the anterior and posterior roof of the notch, a biomechanically weaker ACL may be the reason for disposition to an ACL rupture in patients with a small intercondylar notch. Women have a thinner ACL midsubstance than men of the same height which may be one of the critical etiologic factors that predispose women to an ACL rupture.

Anterior Cruciate Ligament↗

PubMed2006

[Allogenic meniscus transplantation].

OBJECTIVE: Total replacement of the meniscus to reduce pain and improve joint function. INDICATIONS: Symptomatic early arthrosis of the lateral compartment in young patients after loss of the lateral meniscus. Loss of the medial meniscus and anterior knee instability in young, active patients. CONTRAINDICATIONS: Advanced cartilaginous damage. Malalignment of the longitudinal axis. Knee ligament instability. SURGICAL TECHNIQUE: Preparation of the allogenic meniscal transplant. Placement of sutures to the "horn ligaments". Lateral or medial arthrotomy. Osteotomy of the femoral epicondyle with the collateral ligament. Excision of meniscal residues leaving only a narrow outer rim. Holes are drilled from the anterolateral or anteromedial tibial metaphysis to the horn insertions. The horn ligaments are pulled into the drill holes. Fixation of the meniscal transplant by insertion of vertical sutures at the outer rim and joint capsule. Tightening and temporary fixation of the meniscal horn sutures at the exit sites of the drill holes. The function of the transplanted meniscus is evaluated, the tension in the sutures adjusted as required and, finally, the ends are knotted. Refixation of the epicondyle with a 6.5-mm cancellous bone screw. POSTOPERATIVE MANAGEMENT: Active and passive exercises from extension to 90 degrees flexion. Partial loading in a brace in extension on two crutches for the first 6 weeks postoperatively. No full squat for a further 3 months. Sports activities not before the end of the 1st postoperative year. RESULTS: Good results for correct indications with a survival rate of the transplant of 70-80% after 3-7 years and significant improvement of joint function and pain reduction. An effect on the results related to arthroscopically assisted or open technique and/or related to anchorage of the meniscal horns in the bone or soft tissue could not be shown. In biomechanical terms, the stable fixation of the meniscal horns is decisive. Fixation of the periphery of the meniscus to the joint capsule by vertical sutures alone is not sufficient but does play an important role in the incorporation of the meniscal tissue. Anterior cruciate ligament reconstruction should be performed at the same time; correction osteotomy should be performed at a separate operation prior to meniscal allograft transplantation.

Bone Screws↗

PubMed2006

Arthroscopic psoas tenotomy.

Tenotomy may be indicated for psoas tendinitis or painful snapping if conservative treatment remains unsuccessful. Because of significant complications with open techniques, endoscopic operations have been developed. We present a new arthroscopic technique to access and release the psoas tendon from the hip joint. This procedure can be performed in addition to other arthroscopic procedures of the hip joint or alone. To exclude additional hip disease, a diagnostic round of the joint should be completed. After hip arthroscopy of the central compartment has been performed, traction is released and the 30 degrees arthroscope is placed via the proximal anterolateral portal lying on the anterior femoral neck. The medial synovial fold can be identified. This fold lies slightly medially underneath the anteromedial capsule at the level of the psoas tendon. The arthroscope is turned toward the anterior capsule. Sometimes, the tendon shines through a thin articular capsule, or it may even be accessed directly via a hole connecting the hip joint and the iliopectineal bursa at the level of the anterior head-neck junction. If this cannot be done, an electrothermic probe is introduced via the anterior portal to make a 2-cm transverse capsular incision. The tendon is released with the back side of the electrothermic device turned to the iliacus muscle that lies anterior to the psoas tendon. A complete release is achieved when the tendon stumps can be seen gapping at a distance and the fibers of the iliacus muscle are visible. The first 9 patients who underwent surgery performed according to this technique developed no complications, and their hip flexion strength was restored to normal within 3 months.

Arthroscopy↗

PubMed2005

Safe arthroscopic access to the central compartment of the hip.

This technical note describes a new method that allows access to the central compartment of the hip under arthroscopic control via the peripheral compartment with less risk of labral perforation and/or cartilage scuffing. After placement of the anterolateral portal in the peripheral compartment without traction, the anterior head area with the anterior acetabular labrum and the anterior surface of the femoral head are inspected. Under arthroscopic control, a guidewire is introduced through the anterior portal in between the anterior labrum and anterior femoral head cartilage and into the central compartment. The arthroscope is then removed from the anterolateral portal, the hip distracted, and the arthroscope introduced via cannulated instruments over the guidewire into the central compartment. Further portal placement can be controlled arthroscopically.

Arthroscopy↗

PubMed2004

Reconstruction of the medial femoral condyle and medial collateral ligament in total knee arthroplasty using tendoachilles allograft with a calcaneal bone block.

Absence or compromise of the medial collateral ligament (MCL) in conjunction with osseous defects of the medial femoral condyle in total knee arthroplasty (TKA) is a challenging reconstructive problem. Treatment usually requires a highly constrained TKA with or without ligamentous reconstruction. To restore the medial femoral condylar bone and to provide ligamentous stability on the medial side of the knee, the authors present a technique for reconstruction of the medial femoral condyle and MCL using a tendoachilles allograft with a calcaneal bone block. The construct also can be augmented with a semitendinosus tendon autograft. Two illustrative cases and a review of the literature are presented.

Achilles Tendon↗

PubMed2004

Arthroscopic treatment of an avulsion fracture of the ligamentum teres of the hip in an 18-year-old horse rider.

We present the case of an 18-year-old horse rider with an avulsion fracture of the ligamentum teres causing persistent hip pain and locking for 2 years. The patient had no history of major trauma; however, repeated minor hyperabduction injuries occurred. We were able to successfully treat this patient by arthroscopic removal of the bony fragments and two loose bodies and partial resection of the ligamentum teres.

Adolescent↗

PubMed2003

Influence of cage geometry on sagittal alignment in instrumented posterior lumbar interbody fusion.

STUDY DESIGN: Retrospective radiographic evaluation of the sagittal alignment of the lumbar spine in patients undergoing short-segment instrumented posterior lumbar interbody fusion with cage systems of different shape. OBJECTIVES: To determine whether rectangular and wedge-shaped cages have a different influence on the sagittal alignment of the lumbar spine in patients undergoing short-segment instrumented posterior lumbar interbody fusion. SUMMARY OF BACKGROUND DATA: Previous studies of sagittal alignment after posterior lumbar interbody fusion have focused on the impact of intraoperative patient, hip, and knee positioning, as well as instrumentation characteristics on sagittal posture. The influence of the cage shape on indexes of total and segmental sagittal alignment of the lumbar spine is yet unknown. METHODS: Forty-two patients having undergone instrumented short-segment posterior lumbar interbody fusion were reviewed retrospectively. Twenty-two patients (12 women and 10 men, 38-78 years of age) had posterior lumbar interbody fusion with rectangular cages. The fused segments were: 4 at L3-L4, 16 at L4-L5, 11 at L5-S1. Thirteen patients had single- and nine patients double-level fusion. Twenty patients (8 women and 12 men, 34-81 years of age) had posterior lumbar interbody fusion with wedge-shaped cages. The fused segments were: 4 at L3-L4, 15 at L4-L5, 11 at L5-S1. Ten patients had single- and 10 patients double-level fusion. Cages were packed with cancellous bone from the posterior iliac crest and/or bone fragments harvested by laminectomy. All patients had additional pedicle screw fixation. Pre- and postoperative standing lateral radiographs were assessed for segmental and lumbar lordosis as well lumbar and sacral tilt. Data were analyzed with repeated measures analysis of variance. RESULTS The mean follow-up period was 18 months with a minimum follow-up period of 14 months. Mean segmental lordosis of the fused segments showed significant changes between the two implant groups (P < 0.05). Segmental lordosis decreased in the rectangular cage group from 10 degrees to 2 degrees at L3-L4, from 10 degrees to 5 degrees at L4-L5, and from 9 degrees before to 6 degrees after fusion surgery at L5-S1. In the wedge-shaped cage group, segmental lordosis increased from 4 degrees to 7 degrees at L3-L4, from 2 degrees to 8 degrees at L4-L5, and from 9 degrees to 17 degrees at L5-S1. Analysis of changes in lumbar lordosis and lumbar and sacral tilt did not show significant differences though opposite trends: lumbar lordosis decreased from 55 degrees to 48 degrees in the rectangular cage group and increased from 45 degrees to 53 degrees in the wedge-shaped cage group. Lumbar tilt measured 98 degrees before and 102 degrees after surgery in the rectangular cage group and 97 degrees before and 94 degrees after surgery. Sacral tilt measured 44 degrees before and 40 degrees after surgery in the rectangular cage group and measured 42 degrees before and 45 degrees after surgery in the wedge-shaped cage group. CONCLUSIONS: The cage geometry has a significant impact on the alignment of the lumbar spine after instrumented posterior lumbar interbody fusion. With rectangular cages, lumbar lordosis and segmental lordosis of the segments fused decrease; sagittal balance is maintained by compensatory changes of the sacral tilt. Wedge-shaped cages significantly increase segmental lordosis, enhance lumbar lordosis, and therefore should be preferred for restoring sagittal alignment in instrumented posterior lumbar interbody fusion procedures.

Adult↗

PubMed2002

Intra-articular osteochondroma of the posterior cavity of the knee.

A patient with a large intra-articular osteochondroma of the posterior cavity of the knee joint is presented. Preoperative imaging included radiographs and magnetic resonance imaging, which revealed a completely intra-articular, locally expanding, mineralised mass in the intercondylar tunnel and posterior joint cavity. Flexion was limited to 70 deg. The osteochondroma was removed from a posterior approach. Gross and histologic pictures are presented, and the origin and pathogenesis of the tumour are discussed. After removal, the clinical course was benign. Full flexion was regained within 2 months. At the 2-year follow-up, no signs of recurrence were evident on radiographs and magnetic resonance imaging.

Aged↗

PubMed2002

Anatomy and biomechanics of the anterior cruciate ligament.

This article reviews the literature on embryology, anatomy, function, and biomechanics to define the properties of the native ACL. The discussion focuses on the ligamentous architecture and gross anatomy of the ACL including its femoral and tibial insertions as well as its midsubstance passing through the intercondylar fossa. Biomechanical modeling, mechanical and structural properties, and function of the ACL as a primary and secondary stabilizer under non-weightbearing and weightbearing conditions are described.

Anterior Cruciate Ligament↗

PubMed2002

Effects of traction, distension, and joint position on distraction of the hip joint: an experimental study in cadavers.

PURPOSE: To quantify the effects of traction alone and in combination with distension of air in different joint positions in order to find out the conditions for adequate distraction of the hip joint with minimal traction force. TYPE OF STUDY: Experimental cadaver study. METHODS: Eight cadaver hip joints were studied. The cadavers were placed supine on a fracture table and traction was applied in different joint positions for flexion and abduction with and without distension using air. For the measurement, the joint space between the acetabulum and femoral head was separated by 4 different lines characterizing the lateral margin of the acetabulum, the superior portions of the lunate cartilage, and the acetabular fossa. RESULTS: At all measurement lines, distraction of the hip was significantly better when traction and distension were combined. At traction forces from 250 to 300 N, traction plus distension resulted in a 1.59- to 2.25-fold increase of joint distraction compared to traction alone. The maximum effect of distension was achieved between 200 and 250 N. Up to traction forces of 250 N, the joint vacuum force counted for more than half of the total resistance. The effects of flexion and abduction on distraction of the hip were smaller. A trend for better distraction was found for 20 degrees of flexion and a significantly better distraction by avoiding abduction. CONCLUSIONS: High traction forces by breakage of the joint seal can be avoided by distension using air. The passive resistance of the soft tissues increases at higher traction forces. Slight flexion without abduction showed further increase of joint distraction. Reducing the amount of traction may possibly reduce the risk of soft tissue perineal and neurologic injuries.

Adult↗

PubMed2001

Arthroscopic treatment of tumor-like lesions of the knee joint: Localized pigmented villonodular synovitis and ganglion cyst of the anterior cruciate ligament.

We present the arthroscopic treatment of a case of localized pigmented villonodular synovitis that led to increasing restriction of knee flexion and the case of a ganglion cyst within the anterior cruciate ligament causing unspecific pain. Both pathologies could be resected arthroscopically with complete relief of symptoms and no recurrence. In cases with unspecific clinical signs and intra-articular masses shown on magnetic resonance imaging, arthroscopy is the next therapeutic step. Localized tumor-like lesions can often be excised without recurrence in the same session.

Journal Article↗