Matthias Honl

Duration and frequency of every day activities in total hip patients.

Little knowledge about frequency and duration of daily activities in patients after total hip arthroplasty is available. Such information is required for the definition of realistic load collectives for pre-clinical testing of prostheses. It could also be helpful for the quantitative evaluation of surgery outcome with different prosthesis types. The purpose of this study was to develop and apply a system for the determination of frequency and duration of patient activities in their habitual environment and to compare the results to a clinical outcome score (Harris hip score).A portable activity monitoring system (weight 1.6 kg including batteries) was designed using a Palm top computer, 2 inclination sensors for the thigh and calf and one goniometer positioned at the knee joint. An algorithm was developed to identify frequency and duration of the activities lying, sitting, standing, walking and stair climbing from the signals of the 3 sensors. 42 patients participated in the study and were equipped with the system in the morning at their home. Datasets of 31 patients (age 62.5+/-11.5 y) covered more than 6h (9.8 +/- 1.6 h) and were included in the analysis. Prosthesis specific data as well as the Harris hip score were collected. The most frequent patient activity was sitting (44.3% of the time), followed by standing (24.5%), walking (10.2%), lying (5.8%) and stair climbing (0.4%). The median number of steps/stairs was 6048/164. The number of step cycles representing one year in vivo use should, consequently, be increased to 1.1 million. The Harris hip score (91.4 +/- 9.8) correlated significantly with the number of stairs (r(2) = 0.26, p = 0.003) and showed a positive tendency with the number of steps per day. No differences in activity levels between prosthesis specific factors were found.

Orientation of the acetabular component: A COMPARISON OF FIVE NAVIGATION SYSTEMS WITH CONVENTIONAL SURGICAL TECHNIQUE

We compared the orientation of the acetabular component obtained by a conventional manual technique with that using five different navigation systems. Three surgeons carried out five implantations of an acetabular component with each navigation system, as well as manually, using an anatomical model. The orientation of the acetabular component, including inclination and anteversion, and its position was determined using a co-ordinate measuring machine. The variation of the orientation of the acetabular component was higher in the conventional group compared with the navigated group. One experienced surgeon took significantly less time for the procedure. However, his placement of the component was no better than that of the less experienced surgeons. Significantly better inclination and anteversion (p < 0.001 for both) were obtained using navigation. These parameters were not significantly different between the surgeons when using the conventional technique (p = 0.966). The use of computer navigation helps a surgeon to orientate the acetabular component with less variation regarding inclination and anteversion.

Bone-Patellar Tendon-Bone Grafts for Anterior Cruciate Ligament Reconstruction An in Vitro Comparison of Mechanical Behavior under Failure Tensile Loading and Cyclic Submaximal Tensile Loading

Background Secure fixation is an important factor in the success of anterior cruciate ligament reconstruction. Hypothesis There is no difference in the mechanical behavior of reconstructions from method of fixation or method of testing. Study Design Controlled laboratory study. Methods Anterior cruciate ligament reconstructions were performed with bone-patellar tendon-bone grafts in 48 human cadaveric knees. Three different fixation methods (Endobutton, interference screw, suture-post fixation) were compared under failure tensile loading and cyclic submaximal tensile loading. Results No difference was observed in ultimate load among the three techniques. Stiffness of the grafts was significantly lower for the suture technique than for the interference screw technique. Cyclic loading revealed significantly different failure rates: 0% of the Endobutton, 38% of the interference screw, and 100% of the suture-post groups. The relative movement of the femoral bone plug and the migration of the bone plug out of the femoral canal were lowest in the interference screw group. Conclusions The suture-post fixation is not recommended. The interference screw technique showed the best results, but results were age-dependent, suggesting its best use is in younger patients. The Endobutton technique is recommended for older patients. Clinical Relevance Results of testing are useful to the surgeon in making a choice of reconstruction technique.

Intramuscular pressure in the erector Spinae and intra-abdominal pressure related to posture and load

Study Design. Intramuscular pressures in both Erectors Spinae and intra‐abdominal pressures were measured during different holding tasks. Objectives. To investigate the potential for using intramuscular pressure measurements in both Erectors Spinae to better quantitate the role of muscles during different lifting tasks in vivo. Summary of Background Data. Intramuscular pressure and intra‐abdominal pressure were measured previously under isometric and dynamic conditions. However, no previous study systematically has addressed the relation between intramuscular and intra‐abdominal pressures and different loads, tasks, and postures. Methods. Intramuscular and intra‐abdominal were measured simultaneously with microtip pressure transducers in 10 healthy volunteers performing 24 different static holding tasks. Tasks included different weights (10 kg and 20 kg), postures (squat or back lift), and positions of the weight. Results. Intramuscular pressures were dependent on posture. Kyphotic back posture produced intramuscular pressures of 120‐130 mm Hg, compared with the 10‐25 mm Hg produced when volunteers were in the erect position (P < 0.001). Holding a 10‐kg weight at the thighs close to the body produced significantly (P < 0.001) lower intramuscular pressures (25‐32 mm Hg) than that produced by holding it 25 cm in front of the body (47‐56 mm Hg). In all tasks, intramuscular pressures were significantly higher with the 20‐kg weight than with the 10‐kg weight (P < 0.001). Highest values (> 300 mm Hg) were measured when the 20‐kg weight was held in the kyphotic posture above the floor and 25 cm away from the body. Conclusions. Intramuscular pressure measurements in the erector spinae seem to be a valuable tool for quantitating the role of back muscles during different lifting tasks.

The use of water‐jetting technology in prostheses revision surgery—First results of parameter studies on bone and bone cement

Water-jet cutting techniques have been used in industrial applications for many different materials. Recently these techniques have been developed into a revolutionary cutting tool for soft tissues in visceral surgery. The present study investigates the usage of this cutting technology for the revision surgery of endoprostheses. In the first part of the study, samples of bovine bone and acrylic bone cement (PMMA) were cut using an industrial jet cutting device with pure water. Below 400 bar, only PMMA was cut; above 400 bar, bone was also cut, but only pressures above 800 bar resulted in clinically useful rates of material removal (cut depth 2. 4 mm at 10 mm/min traverse speed). In the second part of the study, the effect of adding biocompatible abrasives to the water in order to reduce the required pressure was investigated, resulting in a significantly higher removal of material. At 600 bar, PMMA was cut 5. 2 mm deep with plain water and 15.2 mm deep with added abrasives. The quality of the cuts was increased by the abrasive. Though there was no clear selectivity between bone and PMMA any more, the rate of material removal at similar pressures was significantly higher for PMMA than for bone (600 bar: 1.6 mm cut depth for bone samples, 15.2 mm for PMMA). The measured cut depths with either method were not influenced by a change of the cutting direction with respect to the main direction of the osteons in the bone. However, a reduction of the jet surface angle (90 degrees to 23 degrees ) resulted for bone in a significantly lower cut depth at 600 bar (plain water: 0.62 mm vs. 0.06 mm; abrasive: 1.61 mm vs. 0.60 mm). The laboratory experiments indicate that abrasive water jets may be suitable for cutting biomaterials like bone and bone cement.

Determination of the in vivo loading of the lumbar spine with a new approach directly at the workplace – first results for nurses

OBJECTIVE To determine the magnitude of workplace loading for nurses with and without a history of low back pain. DESIGN A measurement system for the assessment of workplace loading as well as a model for the calculation of lumbo-sacral junction loading was designed and applied to a group of 12 nurses with and without a history of low back pain. BACKGROUND Disagreement exists regarding the key factors in the aetiology of low back pain. Traditionally workplace loading is viewed as the dominant influence. Data for workplace loading in jobs with non-uniform tasks, however, do rarely exist. METHODS A three-dimensional inverse-dynamic and force distribution model as well as the respective data acquisition system was used to assess the workplace loading of 12 nurses from surgical departments of two hospitals. The nurses were assigned to two groups based on their history of low back pain (with/without). Workplace loading was measured continuously for 4 h. RESULTS No differences in workplace loading between nurses with/without a history of low back pain were found. Maximum values of the compressive force at the lumbo-sacral junction were high and well above suggested workplace load limits. High values occurred only during short-time periods (about 0.4% of total shift duration). CONCLUSIONS A system for the assessment of overall workplace loading has been developed. First results for nurses suggest that critical loadings do exist at the workplace, even so they might not be the decisive factor for the development of low back pain. RELEVANCE Preventative measures for low back pain in nursing have to include prevention of critical workplace loading. This approach by itself, however, is probably not sufficient.

Der gepulste Wasserstrahl zur selektiven Knochenzemententfernung in der Revisionsendoprothetik. The Pulsed Water Jet for Selective Removal of Bone Cement During Revision Arthroplasty

Conventional tools used in prosthetic revision surgery have a limited range of action within the narrow cement mantle. Water jet cutting technology permits tiny and precisely controlled cuts, and may therefore be an alternative method of bone cement removal. Our study compares the cutting performance on bone cement (PMMA) and bone of a pulsed water jet and a continuous water jet. The aim of the study was to establish whether selective removal of PMMA is possible. 55 bone specimens (bovine femora) and 32 specimens of PMMA were cut with a continuous and a pulsed water jet at different pressures (40 MPa, 60 MPa) and pulse frequencies (0Hz, 50Hz, 250Hz). To ensure comparability of the results, the depths of cut were related to the hydraulic power of that part of the jet actually impinging on the material. While for PMMA the power-related depth of cut increased significantly with the pulse frequency, this did not apply to bone. The cuts produced in bone were sharp-edged. Since PMMA is more brittle than bone, the water jet caused cracks that enlarged further until particles of bone broke away. Although selective removal of PMMA without doing damage to the bone was not possible at the investigated settings of the jet parameters, the results do show that a pulsed water jet can cut bone cement much more effectively than bone. This is an important advantage over conventional non-selective tools for the removal of bone cement.

Pelvic girdle reconstruction based on spinal fusion and ischial screw fixation in a case of aneurysmal bone cyst.

A case of lytic lesion of the pelvis in a 23-year-old woman is presented. A biopsy led to the diagnosis aneurysmal bone cyst (ABC). Due to the histologically very aggressive growth of the tumor, a low malignant osteosarcoma could not be excluded. In an initial operation the tumour, affecting the sacrum, the iliac crest and the lower lumbar spine was resected. Temporary restabilisation of the pelvic ring was achieved by a titanium plate. The histological examination of the entire tumour confirmed the diagnosis ABC. After 6 months, the MRI showed no recurrence. The observed tilt of the spine to the operated side on the sacral base prompted a second surgical procedure: a transpedicular fixation of L5 and L4 was connected via bent titanium stems to the ischium, where the fixation was achieved by two screws. This construction allowed the correction of the base angle and yielded a stable closure of the pelvic ring. The patient has now been followed for 6 years: the bone grafts have been incorporated and, in spite of radiological signs of screw loosening in the ischium, the patient is fully rehabilitated and free of symptoms. Pedicle screws in the lower spine can be recommended for fixation of a pelvic ring discontinuity.

Der Druckwasserstrahl zum selektiven Abtrag der Synovialis - In-vitro-Studie zur Machbarkeit eines neuen Synovektomieverfahrens

Aim: The selectivity of a water jet (WJ) is already used with clinical advantage in the surgery of liver, brain, kidney and herniated lumbar discs. The aim of the present study was to determine whether a WJ can be used for synovectomy without damaging the joint capsule and the cartilage. Method: 60 human cadaver knee specimens (67 ± 14 years) were dissected into synovial and cartilage samples. They were randomly assessed to four pressure groups (p W = 3; 6; 9; 12 MPa) and three jet surface angles (β = 30; 60; 90°) The nozzle diameter was d D = 0.12 mm, the stand off distance of the jet was s = 10 mm with a feed rate of v V = 2 mm/s. The acquired parameters were depth of the cuts, histological layer, and change of the samples thickness. Result: There was a correlation of the cutting depth and the pressure (p W ), whereas the jet-surface angle (β) showed no correlation. The synovial layer of the cut likewise correlated with the pressure. At p W = 6 MPa the stratum subsynoviale could be cut selectively without damaging the fibrous capsule or the cartilage. The increase of the samples thickness was caused by an interstitial oedema. Conclusion: The different mechanical properties of the joint capsule and the stratum subsynoviale lead to the selective cutting of the water jet. Since the joint capsule was not damaged, the feasibility of WJ synovectomy has been proven. The device coon be used for synovectomy in parts of the joint that are not visible as well as in very small joints.

Aneurysma spurium der A. poplitea nach vorderer Kreuzbandplastik

Der arthroskopische Ersatz des vorderen Kreuzbands ist eine weit verbreitete und relativ komplikationsarme Operationstechnik. Wir berichten über eine Patientin, die bei der arthroskopischen Kreuzbandersatzoperation ein falsches Aneurysma der Poplitealarterie erlitt. Die Poplitealarterie wurde durch die tibiale Fixation mit einer Spongiosaschraube als Pollerschraube verletzt. Die Entwicklung dieser Komplikation in Bezug auf die Fixationsmethode wird diskutiert.Arthroscopic reconstruction of the anterior cruciate ligament (ACL) is a widely performed and relatively safe technique with few complications. We report a case of a woman who incurred a pseudoaneurysm of the popliteal artery during arthroscopic ACL reconstruction. Tibial fixation with a postfixation screw injured the popliteal artery. The development of this complication relating to the fixation method is discussed.