Surgical Anatomy. — There are a few anatomical facts bearing directly on dislocations of tlie patella, to be taken up at this time without entering into the details of the knee-joint, which were considered under fractures of the patella. The pull of the quadriceps is upward and in a direction parallel with the long axis of the femur. The ligamentum patellae lies in the long axis of the tibia and since the axis of the tibia is not the same as that of the femur it will be apparent that the pull of the quadriceps (with the leg extended), is not in line with the long axis of the ligamentum patellae. It is evident, therefore, that when the quadriceps contracts it not only pulls the patella upward but also tends to displace it outward. This tendency toward outward displacement of the patella is normally counteracted by the outer lip of the trochlear surface of the femur and the attachments of the capsule and fascia lata. When the capsule and fascia lata internal to the patella are lax, or when the outer lip of the trochlea is not sufficiently prominent, the bone may be displaced outward on violent contraction of the extensors of the thigh. The angle at which the tibia joins the femur varies considerably in different persons. It is usually greater in women because of the proportionately broader pelvis and greater divergence of the femora. The angle is greater in short stocky persons than in those of tall and slender stature. If the knee be fully extended and the quadriceps relaxed the patella will be found quite freely movable from side to side as well as vertically. If the lower extremity be kept in the same position and the thigh muscles tightened the patella immediately becomes fixed. This is due largely to the vertical groove in the trochlea and the corresponding ridge on the articular surface of the patella. It will thus be seen that although the quadriceps has a lateral displacing action on the patella, yet the contraction of this muscle also tends to prevent lateral displacement (if the fascial attachments and trochlea are normal) by forcing the patella into the groove on the trochlea. The muscles and fasciae attached to the bone often tend to fix it in displacement after dislocation has occurred. The patella may be dislocated in any direction and is not uncommonly found rotated on its axis. If the patella is displaced laterally until it clears the trochlear surface, or the bone is completely rotated on its axis so that the articular face looks forward, the dislocation is said to be complete. If portions of the articular surfaces remain opposed or if the bone stands on edge the condition is incomplete and is spoken of as a subluxation. These distinctions are of degree only, and are more academic than practical. The same may be said of the classifications based on the details of the possible positions occupied by the patella during displacement.
Etiology. — Luxations of the patella constitute less than one percent of all dislocations. Displacement may be in any direction although the external lateral type is by far the most common. The condition may be partial or complete. It is more common in women than in men; in short persons than in tall. Muscular action is often responsible for this luxation, although it may be caused by direct violence. A combination of these two elements is not uncommon.
Symptoms. — Sharp pain occurs at the time the bone is pulled or driven out of place, and unless spontaneous reduction occurs (which is not uncommon) there will be immediate loss of function with deformity which can be readily recognized both by inspection and palpation. Following the accident symptoms of acute traumatic arthritis develop although they are seldom as severe as those accompanying fracture of the patella. The deformity varies with the type of displacement. Recurrence of luxations of the patella are not uncommon and may constitute a most annoying and disabling condition. In many cases the patient will know just what position of the knee or what form of strain is productive of the displacement, and is always on his guard to avoid the condition while using the lower extremity.
Diagnosis. — If the surgeon sees the condition prior to reduction, he may recognize the displacement by the characteristic deformity. Palpation of the parts will readily determine, not only the fact that the patella is displaced but also, the type of luxation present. In instances in which the dislocation has been corrected or spontaneous reduction has taken place, it may be difficult to differentiate the condition from a fractured or luxated semilunar cartilage. A careful history and examination of the parts will usually result in determining which of the two conditions has occurred.
Treatment. — As a rule, little difficulty is experienced in returning the patella to its proper position. The knee should be maintained in complete extension, while the thigh is flexed on the abdomen to relax the quadriceps extensor. If the patella does not then slip back into place of itself, slight manipulation will usually suffice to reduce the luxation. Before manipulation is attempted the surgeon should have learned the relations of the displaced bone by palpation, so that he may cause it to retrace the course taken at the time of the accident. When the patella is found rotated on its vertical axis it is particularly necessary that the surgeon know in which direction rotation has taken place. This is readily determined by palpation of the muscle above, and the ligamentum patellae below. It is extremely rare to encounter difficulty in reduction if the above manipulations be followed out, but should such occur, complete relaxation of the quadriceps may be had under anesthesia. In old, unreduced dislocations of the patella reduction may be impossible by ordinary methods, and under such circumstances it may be necessary to resort to open treatment.
Operative Treatment. — Reduction of recent dislocations of the patella by the open method is rarely necessary. In old luxations and in instances of recurrent dislocations operative treatment is often the only method which will give satisfactory results. In either of these conditions the bone may be exposed by a vertical incision or by the usual U-shaped incision. In old luxations it may be necessary to break up old adhesions and cut through scar tissue before the bone can be returned to its original position.
A number of methods have been advised and employed for the correction of recurrent dislocations. The tubercle of the tibia, with its attached ligamentum patellae, may be chiseled off and reattached to the tibia, internal to its original position, so that the pull of the quadriceps is straightened, and the muscle thus loses its outward displacing action on the patella. Another method consists in plication of the internal portion of the capsule or in the repair of a rent, if one exists, thus securing the inner border of the patella so that it cannot be displaced outward by the pull of the quadriceps. Still another method consists in increasing the prominence of the outer lip of the trochlea by dividing it from the femur and displacing it forward. The first two methods are to be preferred to the last. In any of these operations the most strict asepsis is demanded, especially if the joint is opened.
After-Treatment. — Following reduction, the knee should be put at rest on a ham splint, and measures instituted for the control of the traumatic arthritis. Snug bandaging, and the use of the ice cap will usually be followed by subsidence of swelling within a few days. When the inflammatory reaction has passed, the knee should be strapped with surgeon's plaster to steady the patella, and the patient should be cautioned to avoid unnecessary strains. The position of the knee in which the luxation occurred is particularly dangerous.
Prognosis. — Dislocations, resulting from direct violence are likely to be followed by complete restoration of function, unless the trauma was severe and resulted in injury to the joint greater than that occurring in the ordinary patellar luxation. Dislocations resulting from muscular action are likely to recur at some later date. Recurrent dislocations are usually followed by good results if appropriately operated. In old unreduced dislocations restoration of function may be delayed or incomplete as a result of articular changes occurring while the bone was displaced.
<Callout type="important" title="Proper Positioning">Maintaining the knee in complete extension is crucial to prevent further displacement.</Callout>
<Callout type="warning" title="Anesthesia Risks">Complete relaxation under anesthesia may be necessary if reduction fails, posing risks of complications.</Callout>
Key Takeaways
- Dislocations of the patella are rare but can occur due to direct violence or muscular action.
- Proper positioning and manipulation are key in reducing dislocations.
- Recurrent dislocations may require surgical intervention.
Practical Tips
- Always keep the knee extended during initial treatment to prevent further displacement.
- Use a splint or brace to immobilize the knee after reduction.
- Be cautious of recurrent dislocations, which may need surgical correction.
Warnings & Risks
- Anesthesia is risky and should only be used if necessary for reduction.
- Incomplete reduction can lead to chronic pain and disability.
- Articular changes in old unreduced dislocations can affect long-term function.
Modern Application
While the techniques described here are historical, understanding patellar dislocation remains crucial for modern survival preparedness. The principles of immobilization and proper positioning still apply, and recognizing the signs early can prevent complications.
Frequently Asked Questions
Q: What is the most common type of patella luxation mentioned in this chapter?
The external lateral type is by far the most common, where the patella is displaced outward.
Q: How can a patient recognize if they have recurrent dislocations of the patella?
Patients may know specific positions or strains that cause displacement and are usually cautious to avoid these conditions while using their lower extremity.
Q: What is the importance of maintaining knee extension during initial treatment of a patellar dislocation?
Maintaining knee extension helps prevent further displacement by relaxing the quadriceps muscle, which tends to pull the patella outward.