Sunday, September 8, 2013

Rotator cuff repair - position of immobilization

Optimal shoulder immobilization postures following surgical repair of rotator cuff tears: a simulation analysis.

These authors recognize that there is a high incidence of retear following surgical repair of rotator cuff tears and that there is no consensus on the best immobilization postures.

They used a model of the shoulder to find positions of the shoulder that minimized stresses in the repaired tendon after repair of rotator cuff tears involving the supraspinatus only and the supraspinatus concomitantly with the infraspinatus or subscapularis. 

Perhaps the post important finding of this study are that (1) there is tension in the supraspinatus tendon when it is in a neutral (sling) position and (2) that as the size of the gap repaired increases, the tension in the repair with the arm in a neutral position increases dramatically. Here is a graph we made from their data.

To reduce the tension below 100 N per cm sq for the different gap lengths, increasing degrees of humerothoracic elevation were required as shown in this graph we made from their data.

From these data, one can see that it is very difficult to protect the repaired tendon from stress. A 5 mm tendon tear is a small one indeed, but the arm has to be held in 70 degrees of elevation to reduce the stress below 100 N / cm sq  in a repaired cuff tear of this size - that is very inconvenient position for an arm to be in for six weeks. A 2 cm tear has to be immobilized at 110 degrees of elevation (really inconvenient), according to this model!

A few other comments are in order.The authors' model assumed that the orthotic would eliminate all tension the repaired cuff except that related to the tension coming from stretching of the musculotendinous units. The fact is, however, that when someone wears an abduction brace, they tend to use their shoulder muscles (including the cuff) to position it comfortably on their ipsilateral hip and the brace itself loads the shoulder muscles when the patient moves from a supine to a standing position.

Here's the brace they mention.

The other point is that whereas the tension in the normal cuff tendon is spread over many many fibers, the tension in a repair is applied to a small number of sutures that do not share the load equally as shown here.

Finally, it is critical to understand that when a cuff defect is repaired, the cuff tension is shifted from the intact tendon to the repaired tendon, a situation that favors stress relaxation through failure of the repair.

Failure With Continuity in Rotator Cuff Repair "Healing" The American Journal of Sports Medicine (ASJM) recently published this most interesting study of 13 patients having arthroscopic cuff repairs. The repaired tendon defects were 1-4 cm full thickness tears of the supraspinatus and/or infraspinatus with less than 2 cm of retraction, i.e. these were tears that were relatively small and reparable.

At the time of the repair, tantalum markers were placed in the substance of the tendon. Post operative sequential CT scans were used to measure the distance between each marker and the suture anchor nearest to it.  This 'anchor bead distance' has been shown by the authors to have an uncertainty of +/- 3 mm on repeat positioning and rescanning of patients with cuff repairs. If this distance increases over time after surgery, it indicates separation of the marked segment of the tendon from the tuberosity in which the anchor was placed. 

The authors also obtained sequential MRIs to search for defects in the repaired tendon.

They found that the markers of all repaired tendons retracted away from the suture anchors over the first year. The average retraction was 16.1 mm with a range of 5.7 to 23.2 mm. Tendon retraction correlated with patient age. As reported previously for open repairs, most of the retraction occurred during the early phases of recovery (i.e. 12 weeks). The amount of retraction did not correlate with the Penn score or with the abduction strength. The authors, as have others, suggest  the need for protection of the repair during the early rehab period. However, it is yet to be determined which post operative protocol is ideal.

It is worth pondering why this retraction might occur. When we look a chronic cuff defect, such as the one below, there is loss of some of the length of the torn tendon due to resorption and retraction. Thus  in order to approximate the torn edge to the footprint at the tuberosity, we place the repaired tendon under greater tension than the intact tendon on either side of it. Therefore, with either static or dynamic loading the pull of the cuff muscles is preferentially applied to the repaired tendon. This would tend to accentuate the problem of suture tension overload encountered during recovery. Perhaps if the resulting creep of the tendon away from the repair site took place at a slow rate, it would allow the body to 'backfill' the resulting gap resulting in 'failure with continuity'.

As interesting as the data on retraction are, the more interesting finding is that 30% of the shoulders had recurrent defects, even though these tears seemed eminently reparable. The shoulders with recurrent tears had lower Penn scores than those with intact cuffs at 52 weeks. Patients with larger tears had a greater chance of having a recurrent defect, although all of the tears repaired in this series would generally be classified as small. The observation of tear recurrence after repair is consistent with previous observations (here and here and here and here) and with the report in 1991 by Harryman, that a substantial number of repaired cuffs do not remain intact after surgery. For example, Harryman found that after open repair of cuffs similar to those in this study, 20% of the shoulders had recurrent defects by ultrasound at 5 years after surgery (he also found that 60% of repaired large tears had recurrent defects at 5 years). 

So once again we are faced with the fact that even in the hands of very experienced surgeons using the most modern repair methods, recurrent defects after repair are common (4 out of 13).

On reflection of all of the above, it seems that a stress relaxation hypothesis may be consistent with the observations.

Consider this diagram of a cuff tear where the orange part of the cuff has pulled away from the blue tuberosity leaving the red portions of the cuff intact.

The surgeon repairs the torn (orange) part of the cuff to the tuberosity, but in doing so, takes the normal tension off of the intact (red) portions of the cuff and causing the repaired portion to support the load applied by the cuff musculature.

Stress relaxation must occur so that the normal portions of the cuff are under physiologic load. This can happen by recurrence of the cuff defect, as diagrammed below (this may be the situation in older individuals with larger cuff defects)

or by 'failure in continuity' in which the torn (orange) and intact (red) portions of the cuff progressively return to their original position, but that new regenerative tissue (green) tissue forms as the edge of the torn tendon pulls away from the footprint (this may be the situation for younger patients with smaller defects).

As we know some cuff tears are like the wall in Frost's poem - they just don't want to be repaired


Robert Frost

Something there is that doesn't love a wall,
That sends the frozen-ground-swell under it,
And spills the upper boulders in the sun,
And makes gaps even two can pass abreast.
The work of hunters is another thing:
I have come after them and made repair
Where they have left not one stone on a stone,
But they would have the rabbit out of hiding,
To please the yelping dogs. The gaps I mean,
No one has seen them made or heard them made,
But at spring mending-time we find them there.
I let my neighbor know beyond the hill;
And on a day we meet to walk the line
And set the wall between us once again.
We keep the wall between us as we go.
To each the boulders that have fallen to each.
And some are loaves and some so nearly balls
We have to use a spell to make them balance:
'Stay where you are until our backs are turned!'
We wear our fingers rough with handling them.
Oh, just another kind of out-door game,
One on a side. It comes to little more:
There where it is we do not need the wall:
He is all pine and I am apple orchard.
My apple trees will never get across
And eat the cones under his pines, I tell him.
He only says, 'Good fences make good neighbors'.
Spring is the mischief in me, and I wonder
If I could put a notion in his head:
'Why do they make good neighbors? Isn't it
Where there are cows?
But here there are no cows.
Before I built a wall I'd ask to know
What I was walling in or walling out,
And to whom I was like to give offence.
Something there is that doesn't love a wall,
That wants it down.' I could say 'Elves' to him,
But it's not elves exactly, and I'd rather
He said it for himself. I see him there
Bringing a stone grasped firmly by the top
In each hand, like an old-stone savage armed.
He moves in darkness as it seems to me~
Not of woods only and the shade of trees.
He will not go behind his father's saying,
And he likes having thought of it so well
He says again, "Good fences make good neighbors."


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