Jan Korner

Proximal humeral fractures: how stiff should an implant be? A comparative mechanical study with new implants in human specimens.

BackgroundThe objective of this study was to determine the in vitro characteristics of the clinically used and newly developed implants for the stabilization of proximal humeral fractures under static and cyclic loading. The goal was to optimize implant stiffness for fracture stabilization even in weak bone stock.MethodsIn a laboratory study using 35 fresh human humeri, the specimens were randomized into 5 groups, which included the clinically used humerus T-plate (HTP), the cross-screw osteosynthesis (CSO), the unreamed proximal humerus nail with spiral blade (UHN), the recently developed Synclaw Proximal Humerus Nail (Synclaw PHN) and the angle-stable Locking Compression Plate Proximal Humerus (LCP-PH). The implant stiffness was determined for three clinically relevant load cases: axial compression, torsion and varus bending. In addition, a cyclic varus-bending test was performed to determine the implant properties under cyclic loading.ResultsIn contrast to a rather elastic and minimally invasive implant(LCP-PH), the conventionally designed ones (Synclaw PHN, CSO, HTP, UHN) showed rather high stiffness values under static loading. In cyclic loading, a strong decrease in stiffness (p<0.05) was found for the rigid implants HTP and UHN. In comparison with the other implants, only the elastic implant (LCP-PH) showed a significantly lower load reduction in a weak bone stock (17±6.2%).ConclusionThe high initial stiffness of rigid implants led to an early loosening and failure of the implant-bone interface under cyclic loading. Implants with low stiffness and elastic characteristics, however, appear to minimize the peak stresses at the bone-implant interface, making them particularly suitable for fracture fixation in osteoporotic bone.

A biomechanical evaluation of methods of distal humerus fracture fixation using locking compression plates versus conventional reconstruction plates.

Objectives: To examine the biomechanical behavior of 2 techniques of double-plate osteosynthesis for fractures of the adult distal humerus using conventional reconstruction plates and locking compression plates. Design: Basic science study. Setting: Experimental in vitro study. Patients/Participants: Forty fresh-frozen human distal humeri specimens. Intervention: Four matched groups with 10 humeri each, median age 74 years (46–95), were created using similar bone mineral density values. Two standard configurations of double-plate osteosynthesis (dorsal or 90° configuration) with either conventional reconstruction plates or locking compression plates were studied for biomechanical properties of the constructs. A fracture model with a 5-mm supracondylar osteotomy gap simulating metaphyseal comminution (AO type 13-A3.3) was used. Main Outcome Measurement: Stiffness testing of the constructs in anterior/posterior bending, torsion, and axial compression loading. Evaluation of alterations of the bone–implant interface and failure patterns under cyclic loading and strength testing. Results: The study demonstrates that primary stiffness in anterior/posterior bending and torsional loading is significantly increased by using locking compression plates in a 90° configuration (P < 0.05) as compared with dorsally applied plates. The differences between the different plate types are insignificant if applied in the same configuration. It is demonstrated that none of the tested implants failed under cyclic loading within the number of cycles expected for 3 months of use. The bone–implant interface is less likely to fail during strength testing with locking compression plates. Conclusion: The biomechanical behavior of the osteosynthesis depends more on plate configuration than plate type. Advantages of locking compression plates are only significant if compared with dorsal plate application techniques. Nevertheless, locking compression plates are helpful supplementary tools for achieving primary stable fracture fixation. This might be of considerable clinical relevance in patients with diminished bone mineral quality or in the presence of metaphyseal comminution.

Where should implants be anchored in the humeral head

To determine histomorphometric and bone strength distribution of the proximal humerus, analyses were done on 24 freshly harvested human cadaveric humeri. Median ages of 46 and 69 years were recorded respectively for the male group (n = 11; minimum, 34 years; maximum, 76 years) and the female group (n = 13; minimum, 46 years; maximum, 90 years). The humeral head was sliced into four equal horizontal levels (Levels 1–4). Five regions of interest were defined in each cutting plane: anterior, posterior, lateral, medial, and central. Histomorphometric analyses evaluated structural parameters (tissue volume to bone volume ratio, trabecular thickness), connectivity (number of nodes, node to node length), and trabecular orientation (mean bone length). The peak values of histomorphometric parameters and bone strength were identified for the cranial section and decreased caudally. The medial and dorsal aspects of the proximal humeral head were found to be the areas of highest bone strength. The trabecular network formed a pattern that connected the center of the gleaned cavity. The structural and connectivity parameters, bone strength, and trabecular orientation showed region- and level-related characteristics. Knowledge of distribution, microstructure, and quality of bone in the humeral head allows the remaining bone stock to be used effectively, even in elderly patients, with a minimally invasive approach and maximum mechanical stability.

Mechanical comparison in cadaver specimens of three different 90-degree double-plate osteosyntheses for simulated C2-type distal humerus fractures with varying bone densities.

Objectives: To investigate the bone-implant-anchorage of 90-degree double-plate osteosynthesis in simulated complete intra-articular distal humerus fractures using conventional reconstruction plates (CRP), locking compression plates (LCP), and distal humerus plates (DHP), depending on the bone mineral density (BMD) of the cadaver specimens. Methods: Groups (CRP, LCP, DHP, n = 8; LCP, DHP, n = 13) in distal humerus cadaver bones were created based on BMD. The fracture model was an unstable intraarticular distal humerus fracture with a transverse osteotomy gap representing metaphyseal comminution (AO type 13-C2.3). Flexion and extension stiffness as well as cycles until failure due to screw pullout under cyclic loading were evaluated. Estimates of BMD values, below which failure was likely to occur, were determined. Results: Stiffness values were not significantly different between groups (extension: P = 0.881, flexion: P = 0.547). Under cyclic loading, consistent screw pullout failure occurred at BMD values below about 400 mg/cm3 for CRP and below about 300 mg/cm3 for LCP constructs. Comparing BMD-matched groups of 8 and 13 specimens respectively, the failure rate was significantly lower for the DHP (0/8) than for the CRP (5/8; P = 0.026) and tended to be lower for the DHP (0/13) as compared to the LCP (4/13; P = 0.096). Conclusion: Bone-implant anchorage was different between locking and nonlocking plate constructs and depended on BMD. While in good bone quality implant choice was not critical, both locking plates provided superior resistance against screw loosening as compared to the CRP at low BMD values (<420 mg/cm3). Based on our laboratory results, we conclude that locking plates such as the LCP and DHP are constructs designed to keep anatomical reduction in the presence of comminution and poor bone quality in a low intra-articular fracture of the distal humerus.

Fracture-dislocations of the elbow joint--strategy for treatment and results.

Abstract Between January 1993 and December 1996, 41 patients with fracture dislocation of the elbow joint were treated in our department. In 28 patients (median age 46 years, range 15–77 years; 16 male, 12 female), a clinical and radiological follow-up was obtained after median 34 months (range 12–59 months). In addition to the humero-ulnar dislocation, isolated fractures were present in 13 patients and combined fractures in 15 (all with involvement of the radial head). Primary neurological deficits were found in 7 and open fractures in 3 patients. In 7 patients, primary definitive surgical therapy was carried out by open reduction and internal fixation. A two-step surgical management (initial closed reduction and immobilization, 5 patients with external fixator, 7 with plaster; secondary open surgical procedure) was performed in 12 and conservative treatment in 9 patients. According to the Leipzig Elbow Score, taking subjective, clinical and radiological criteria into consideration, 4 patients achieved ‘excellent’ and 5 patients a ‘good’ result. Ten patients were scored ‘moderate’ and 9 ‘poor’. The rate of secondary complications necessitating revision was 36%. Poor results were primarily caused by extensive initial soft-tissue damage, delayed definitive surgical therapy, and ectopic heterotopic ossification. In contrast, fracture localization and degree of arthrosis were not of significant importance for the final outcome. In fracture dislocations, the goal is a primary definitive surgical treatment aiming for early postoperative physiotherapy.

Die gekreuzte Schraubenosteosynthese proximaler Humerusfrakturen

ZusammenfassungIm Zeitraum zwischen 4/1997 und 10/1999 wurden 31 Patienten mit dislozierten proximalen Humerusfrakturen mit einer gekreuzten Schraubenosteosynthese operativ versorgt. Bei diesem Operationsverfahren werden 2–3 Kleinfragmentschrauben über einen deltoidopektoralen Zugang vom Schaftfragment aus überkreuzend ventral und dorsal im Humeruskopf platziert. Bei den 2-Segmentfrakturen wird zusätzlich eine Zuggurtung angelegt, bei den 3-Segmentfrakturen das Tub. majus zusätzlich mit 2 Schrauben fixiert. 21 Patienten (14 w, 7 m, Altersmedian 62 Jahre, 18–86) konnten nach einem medianen Follow-up von 18 Monaten (10–29) klinisch und radiologisch nachuntersucht werden. Dabei handelte es sich um 10 2-Segment- und 11 3-Segmentfrakturen. Die Ergebnisse im Constant-Score ergaben bei 15 Frakturen sehr gute und gute Ergebnisse, in 3 Fällen befriedigende und bei 3 Patienten schlechte Ergebnisse (1-mal 2-Segment-, 2-mal 3-Segmentfrakturen). Die Komplikationsrate lag bei 29% (3 Patienten mit frühzeitiger Schraubenentfernung wegen Kopfperforation, 2 mit sekundärer Prothesenimplantation bei Humeruskopfnekrose und 1 mit Redislokation der Fraktur). Die gekreuzte Schraubenosteosynthese stellt eine Alternative bei der Versorgung dislozierter proximaler Humerusfrakturen dar und ermöglicht eine frühfunktionelle Nachbehandlung.AbstractBetween March 1997 and October 1999 thirty-one patients with displaced proximal humeral fractures were treated with crossed screw osteosynthesis. Insertion of the screws was realized by using a deltoideo-pectoral approach placing the screws anteriorly and posteriorly in a crossed manner from the distal fragment into the humeral head. Additionally, in all two-part-fractures a tension band was applied. In all three-part-fractures, the greater tuberosity was reattached by additional screws. In 21 patients (14 female, 7 male, median age 62 years, 18–86) a clinical and radiological follow-up (median 18 months, 10–29) was obtained. Fractures were classified as two-part-fractures in 10 patients and as three-part-fractures in 11 patients. According to the Constant-Score, “excellent” and “good” results were achieved in 15 patients, “moderate” results were found in 3 patients. However, in 3 patients results were only “poor” (1 two-part-, 2 three-part-fractures). The complication rate was 29% (premature hardware removal due to head perforation in 3 cases; humeral head necrosis necessitating prosthetic replacement in 2 patients; secondary displacement in 1 case). Crossed screw osteosynthesis represents an justified alternative in the surgical treatment of displaced proximal humeral fractures permitting early functional therapy.

Tibiakopfplateaufrakturen – Erste Erfahrungen mit einem resorbierbaren Knochenzement zur Augmentation

ZusammenfassungIm Zeitraum von 10/96 bis 01/99 wurde bei insgesamt 29 Patienten (16 Frauen, 13 Männer; Alter Median 56,Spannweite 22–86 Jahre) mit lateralen Tibiakopffrakturen (5 B1-, 13 B2- und 11 B3-Frakturen nach der AO-Klassifikation) eine Osteosynthese in Form einer arthroskopisch, radiologisch gestützten Reposition mit perkutaner Verschraubung (16-mal) oder einer offenen Reposition und Plattenosteosynthese (13-mal) durchgeführt.Das Patientenkollektiv bestand aus: 15 Patienten (7 Frauen, 8 Männer;Alter Median 41,Spannweite 22–86 Jahre), die von 10/96 bis 12/97 retrospektiv erfasst und nach median 11 Monaten (9–22) klinisch und radiologisch nachuntersucht werden konnten.14 Patienten (9 Frauen,5 Männer;Alter Median 56,Spannweite 27–84 Jahre) wurden von 01/98 bis 01/99 prospektiv erfasst und nach 6 Monaten nachuntersucht.Die Impressionszone wurde insgesamt 11-mal mit autologer Spongiosa und 9-mal mit einem resorbierbaren Knochenzement (Norian SRS) augmentiert. In 9 Fällen war wegen des geringen Defektes bzw. eines Spaltbruchs keine Augmentation erforderlich.Im Lysholm-Score und im röntgenologischen Ergebnis zeigten sich in allen Gruppen überwiegend gute bis sehr gute Ergebnisse ohne Unterschiede bezüglich der Augmentationsformen. In der Norian SRS-Gruppe war die Dauer der Teilbelastung sowie die Behandlungsdauer deutlich kürzer.Nach den bisherigen Erfahrungen eignet sich der injizierbare neue Knochenzement aufgrund der günstigen Applikationsform und der hohen Primärstabilität zur Augmentation bei Impressions- bzw. Impressions-/Depressionsfrakturen.AbstractBetween October 1996 and January 1999,29 patients (f:16,m:13,age: 22–86) with fractures of the lateral tibial plateau were operated on arthroscopic,fluoroscopic control or were treated with open reduction and internal fixation. 15 of them were retrospective and 14 prospective analysed.The metaphyseal defect after elevation of the depressed fragment was augmentated in 11 cases with autologeous spongeous bone grafting,in 9 cases with biodegradable bone cement (Norian SRS).Augmentation was unnecessary in 9 cases.The results according to the Lysholm score and the radiological results were good or excellent.Concerning the kind of augmentation no difference was noted. In the Norian SRS-group the duration of postoperative treatment was shorter than in the other group.The duration of partial weight bearing was shorter too.The results of the present study suggest that an injectable calciumphosphate cement may be a competent material for augmetation in lateral tibial plateau fractures because of the application form and the initial high mechanical stability.

Bilateral posterior fracture-dislocation of the shoulder caused by an epileptic seizure – Diagnostic, treatment and result

SummaryThe case of an 39-year-old man is presented, who sustained a bilateral locked fracture dislocation of the shoulders occurring during an epileptic seizure. Radiographs demostrated a compression-fracture of the anteromedial aspect of the humeral head bilaterally (reversed Hill-Sachs-lesions). Additionally, fractures of the lesser and greater tuberosity were diagnosed at the right site. Open reduction and internal fixation was performed in both shoulders within 12 hours. 6 months later the patient has no complaints with a free range of motion. Diagnostics, treatment and result are discussed in context with the literature.ZusammenfassungEs wird der Fall eines 39 jährigen Patienten beschrieben, der sich im Rahmen eines Grand-mal-Anfalls eine fixierte, bilaterale posteriore Schulterluxationsfraktur zuzog. Beidseits lagen große „reversed Hill-Sachs-lesions“ vor, rechts bestanden zusätzlich dislozierte Frakturen von Tuberculum majus und minus. Beide Schultern wurden nach entsprechender Diagnostik am Unfalltag offen reponiert, die Impressionen angehoben und mit einem resorbierbaren Knochenzement (Norian SRS) unterfüttert, sowie die Frakturen osteosynthetisch versorgt; 6 Monate postoperativ war der Patient beschwerdefrei bei freier Beweglichkeit in beiden Schultergelenken. Anhand dieses Beispiels und der Literatur werden Diagnostik und Behandlungsstrategie bei hinteren Schulterluxationen dargestellt.

Arthroscopic-Assisted Simultaneous Reconstruction of the Posterior Cruciate Ligament and the Lateral Collateral Ligament Using Hamstrings and Absorbable Screws

Arthroscopic-assisted simultaneous reconstruction of the posterior cruciate ligament (PCL) and the lateral collateral ligament (LCL) using hamstring tendon grafts is described. The femoral tunnel is drilled through an incision over the medial femoral condyle and the tibial tunnel through the same skin incision used for harvesting the tendon graft. PCL reconstruction is performed using a 4-strand hamstring tendon graft and absorbable screw fixation. The tendon of the semitendinosus muscle of the uninvolved knee is used as a lateral loop for LCL reconstruction. After pulling the transplant through the fibular head, femoral fixation of the loop is made with an absorbable screw.

Sind winkelstabile Plattensysteme mit elastischen Eigenschaften für die Stabilisierung der Oberarmkopffraktur vorteilhaft? / Eine in-vitro biomechanische Untersuchung

Abstract Winkelstabile Platten werden mit zunehmender Häufigkeit zur Stabilisierung von Oberarmkopfbrüchen verwendet. Rigide Implantate führen bei osteoporotischen Knochenverhältnissen u. U. aber häufiger zum Versagen. Um den Effekt der Implantatelastizität zu beurteilen wurden in einer in-vitro Studie die biomechanischen Eigenschaften eines rigiden und eines elastischen winkelstabilen Plattensystems vergleichend analysiert. An 8 Humeruspaaren wurde eine instabile subkapitale Fraktur simuliert. Die Proben wurden axial- und torsions-belastet. Analysiert wurden die Steifigkeit, das Setzverhalten unter Dauerlast und die Versagensbelastung. Das elastische Plattensystem kennzeichnete sich durch eine geringere Torsionssteifigkeit und eine größere Verformung unter Axial- und Torsionsbelastung. Die Proben versagten früher als beim rigiden Plattenystem. Unter biomechanischen Gesichtspunkten bieten Implantate mit elastischen Eigenschaften am Oberarmkopf somit keine Vorteile. Are angle-fixed implants with elastic properties advantageous for the internal fixation of proximal humerus fractures? There is a recent interest for the use of angle-fixed plates in the management of proximal humerus fractures. Rigid implants might be associated with an increased risk of cutting-out. In order to analyse the potential beneficial effects of the implant elasticity on fracture fixation, the biomechanical properties of a rigid and an elastic angle-fixed plating system were assessed in an experimental study. An unstable fracture of the surgical neck was created in 8 pairs of human humeri. Specimens were subjected to axial loading and torque. Stiffness, subsidence and load to failure were assessed. The implant with elastic properties was characterized by a lower torsional stiffness and a higher subsidence during axial loading and torque. This implant failed at lower loads than the rigid implant did. Elastic implant properties of angle-fixed plates have shown not to be advantageous for the management of fractures of the proximal humerus.