02/11/2009
AO Technical Commission Approved

EPOCAa Versatile Prosthesis System

EPOCAa Versatile Prosthesis System Serving as an Anatomical Substitute of the Shoulder Joint in Traumatic and Degenerative Conditions

The EPOCA shoulder arthroplasty system is a versatile prosthetic system serving as an anatomical substitute of the shoulder joint in traumatic and degenerative indications. The system is able to restore glenohumeral kinematics and facilitates anatomical reconstruction of the proximal humerus.

The system consists of a finnless stem of different sizes in a cemented or a press-fit version. The stem is coupled with the head via a unique double eccentric disc. This eccentric disc allows for an independent adjustment of the medial and posterior offset in respect to the shaft. The head sizes grow linearly with a fixed ratio between the head height and radius. The EPOCA shoulder arthroplasty system also comprises of a resurfacing option and a polyethylen glenoid system, which is compatible with all other components. The glenoid system allows a hybrid fixation with shell screws or cementless application with a metal back glenoid. For rotator cuff insufficiencies there is a reco glenoid providing a stable fulcrum despite cuff dysfunction (Fig 1).

In general, the stemmed implants could be used in all conditions, but with the advent of resurfacing implants, the main indication for stemmed implants is in the treatment of irreparable fractures of the proximal humerus and in posttraumatic conditions with advanced joint destruction. The treatment of proximal humeral fractures is still challenging and it is not possible to reliably reconstruct all fractures. Especially severely destroyed humeral head fractures, ie, head splitting fractures, cannot be reduced and stabilized adequately. A second unsolved and widespread problem are the 4-part fractures in the anatomical neck with a very small, often less than 15 mm thin, osteoporotic head fragment. Even with modern angular stable fixation systems plus additional cerclage sutures on the rotator cuff failures like early secondary dislocations occur too often. This is not surprising because there is simply not enough bone to resist the dislocating forces. In these situations the primary fracture prosthesis is the only reasonable treatment option.

Fracture situations are characterized by the fact that many landmarks are destroyed. An ideal prosthesis should help the surgeon to find the original anatomical relations. The implant should be adjustable and individually adaptable but parameters with a low variance can and should be standardized. This not only simplifies the use, but also avoids unnecessary complications and contributes to a reduction of unnecessary components.

Fig 1 EPOCA shoulder arthroplasty system.

The EPOCA philosophy is based on anatomical studies [1]. Besides the medial and the trochanter majus offset, the retrotorsion, as well as the size of the humeral head and the humeral shaft show a large variance and are therefore adaptable in the EPOCA system. On the other hand the inclination of the humeral head, as well as the relation between the humeral height and radius show only a small variance and are therefore standardized.

While the dimensions of the prosthesis components can be easily determined in general, the correct position of the prosthesis concerning height and retrotorsion poses problems, because important references are destroyed by the fracture. Since posteromedially the fracture is usually simple, reference can be taken from this area. The prosthesis height is determined by the length of the posteromedial metaphyseal extension which is still attached to the humeral head (Fig 2ab). This length can be measured easily and defines the gap between the humeral shaft and the head on the medial side. Concerning retrotorsion a standardized adjustment to fixed references, thus, eg, the forearm axis, is not adequate. To restore the correct retrotorsion for the given patient is difficult in fracture conditions due to the missing landmark. For this reason the EPOCA stem provides a special, pronounced calcar design. This anatomical design mimics the contour of the medial calcar and the medullary canal. Using the correct size of the stem leads to a self rotation of the stem with an automatic adjustment of the retrotorsion. In addition, it allows a cementless press-fit implantation, in particular fracture situations. In combination with the unique double eccentric cam the head is freely regulated in any position.

 

Fig 2ab Posteromedial metaphyseal extension attached at the humeral head. This short calcar segment determines the height of the prosthesis on the medial side.


In addition, the correct implantation of the prosthesis the postoperative result decisively depends on the healing of the tubercle. Often secondary dislocations or resorptions are observed, so that the rotator cuff is not able to transmit its forces to the humerus anymore. This contributes to arguments in favor of inverse implants for the treatment of acute fractures. Reduction and stable fixation of the tubercles can be achieved very well with two steel cables. These cables can be passed through the tubercle and two holes in the stem in order to embrace and compress the tubercles against the stem. In comparison to sutures this technique shows a fixation five times stronger. The tubercle should be lined with cancellous bone graft harvested from the retrieved humeral head in order to improve primary stability and healing to the shaft. This allows early rehabilitation and lowers the incidence of dislocated tubercle [2, 3] (Fig 3).

In contrast to fracture conditions, degenerative conditions present differently. In omarthrosis the main pathology is defined by the loss of cartilage coverage. Hence, the prosthetic substitute should limit itself only to the exchange of the damaged cartilage. The original bone stock of the humeral head is thereby preserved and admits all options of revision surgery if necessary. Therefore the resurfacing head is an excellent supplement to the stem in degenerative and posttraumatic conditions.

 

61-year-old male with a 4-part-fracture of the humeral head (head-splitting fracture).

Case provided by Norbert P Sdkamp, Martin Jaeger, Freiburg, DE, Ralph Hertel, Bern, CH

Fig 3ac Fracture situation in conventional x-rays and CT scan.

Fig 3de Implantation of a fracture prosthesis type EPOCA.


Bibliography

  1. Hertel R, Knothe U, Ballmer FT (2002) Geometry of the proximal humerus and implications for prosthetic design. J Shoulder Elbow Surg; 11(4):331338.
  2. Krause FG, Huebschle L, Hertel R (2007) Reattachment of the tuberosities with cable wires and bone graft in hemiarthroplasties done for proximal humeral fractures with cable wire and bone graft: 58 patients with a 22-month minimum follow-up. J Orthop Trauma; 21(10):682686.
  3. Mehlhorn AT, Schmal H, Sdkamp NP (2006) Clinical evaluation of a new custom offset shoulder prosthesis for treatment of complex fractures of the proximal humerus. Acta Orthop Belg; 72(4):18.

Fig 3fg Clinical results 6 months postoperatively.


The EPOCA resurfacing head distinguishes itself not only by its anatomical geometry and its very thin surface, but also by its unique fixation design. A central crown anchors the hydroxyapatite coated prosthesis in a press-fit technique in the peripheral parts of the humeral head. In contrast to the central area which is used by most pegs fixed cups the peripheral area shows a better cancellous bone quality especially in osteoporotic conditions. To date, loosening of the EPOCA resurfacing head has not been observed in larger series (Fig 4).

 

67-year-old female with a primary omarthrosis on the right side.

Case provided by Norbert P Sdkamp, Martin Jaeger, Freiburg, DE, Ralph Hertel, Bern, CH

Fig 4ab Fracture situation in conventional x-rays.

Fig 4cd Implantation of a resurfacing head type EPOCA.


All humeral components can be combined with a glenoid for total joint replacement. The glenoid itself ensures congruent glenohumeral implant surfaces to avoid point contact and to achieve a normal range of motion. It is possible to perform a hybrid fixation with shell screws or to use a press-fit, very thin metal back glenoid. The latter is recommended in conditions of poor bone quality or major posterior wear and distinguishes itself by a minimal lateralization.

The EPOCA shoulder arthroplasty system is a rational, versatile, and valuable supplement in the treatment of humeral head fractures as well as in posttraumatic and degenerative conditions.

 

Fig 4ef Clinical results 6 months postoperatively.

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