Sir,
I read this paper with interest. Despite some of the limitations being mentioned in the
discussion there are some further points that are not fully explained or
evaluated:
1. The concluding statement in the abstract claims that this study
demonstrates that "carefully-selected patients aged 50 years or over can
achieve similar results to those in younger patients". Considering the
methods section states that the sole inclusion criteria for this study
were patients aged over 50 years and primary anterior cruciate ligament
(ACL) reconstruction how were the patients 'carefully selected'?
2. The tensile strength of a native human ACL is approximately 1925 to 2160 N
and that of a reconstructed ACL considerably less, as evidenced by in
vitro and in vivo studies.1,2 In vivo absolute strain
experienced by the ACL is related to the body weight and since the tensile
strength of the reconstructed ACL is relatively fixed, lighter patients
will afford a greater ‘redundancy’ due to the lower strain environment
they impart upon the graft. Was there any evaluation of the patient weight
in this study?
3. The third paragraph of the methods section details the assessment of range
of knee movement, the Lachman and pivot shift tests pre- and post-
surgery. It is unclear exactly who did these evaluations. The
reproducibility of these clinical tests is variable and if more than one
clinician was involved for the study, what were the inter- and intra-
observer error and the associated kappa values?3,4
4. In addition to the above point, how was the pivot shift test
perfomed? When a patient is fully awake, eliciting and detecting a pivot
shift can be problematic, with up to 50% loss of accuracy.5-7 Thus
it has been reported that this test should normally be done under
anaesthetic and graded I to III.8
5. The study uses the subjective UCLA/IKDC/Lysholm/Tegner tests as
stated in the third paragraph of the methods section. Patients who have undergone
an ACL reconstruction demonstrate substantial weakness of the quadriceps
femoris muscle.9-13 Was there any objective measure of
hamstring/quadriceps mass/strength used? Considering the age group of the
patients in the study group, one may expect a wide variation in muscle
mass. Further, do the authors feel that a mean follow up of 72 months is
sufficient to adequately compare the outcome of these patients with that of
younger subjects?
6. The study reports that the pre-operative subjective scores were
obtained in a retrospective manner from reading the medical records. Do
the authors agree that this is a potential source of bias of relevance to
the outcome of this study?
7. The penultimate paragraph of the discussion states that the study
cohort could be ‘compared only to historical controls’. No data are
reported from these historical controls. Were these controls matched for
age, rehabilition regime and pre-operative function?
8. In light of the above points, I feel a degree of caution should be
given to the statement of the final paragraph, that the outcome of ACL
reconstruction in patients over 50 years is similar to that in younger
patients.
B.A. Rogers, MA, MSc, MRCS,
Specialist Registrar, Trauma and Orthopaedics,
St George's Hospital,
London, UK.
1. Liu SH, Kabo JM, Osti L. Biomechanics of two types of bone-tendon-bone graft for ACL reconstruction. J Bone Joint Surg [Br] 1995;77-B:232-5.
2. Smith BA, Livesay GA, Woo SL. Biology and biomechanics of the
anterior cruciate ligament. Clin Sports Med 1993;12:637-70.
3. Miller B. Accurate interpretation of the Lachman test. Clin
Orthop 1988;232:309-11.
4. Noyes FR, Grood ES, Butler DL, Malek M. Clinical laxity tests and
functional stability of the knee: biomechanical concepts. Clin Orthop 1980;146:84-9.
5. Donaldson WF III, Warren RF, Wickiewicz T. A comparison of acute
anterior cruciate ligament examinations: initial versus examination under
anesthesia. Am J Sports Med 1985;13:5-10.
6. Noyes FR, Grood ES, Butler DL, Raterman L. Knee ligament tests:
what do they really mean? Phys Ther 1980;60:1578-81.
7. Noyes FR, Grood ES, Cummings JF, Wroble RR. An analysis of the
pivot shift phenomenon: the knee motions and subluxations induced by
different examiners. Am J Sports Med 1991;19:148-55.
8. Jakob RP, Stäubli HU, Deland JT. Grading the pivot shift: objective tests with implications for treatment. J Bone Joint Surg [Br] 1987;69-B:294-9.
9. Arvidsson I, Eriksson E, Häggmark T, Johnson RJ. Isokinetic
thigh muscle strength after ligament reconstruction in the knee joint:
results from a 5-10 year follow-up after reconstructions of the anterior
cruciate ligament in the knee joint. Int J Sports Med 1981;2:7-11.
10. Seto JL, Orofino AS, Morrissey MC, Medeiros JM, Mason WJ.
Assessment of quadriceps/hamstring strength, knee ligament stability,
functional and sports activity levels five years after anterior cruciate
ligament reconstruction. Am J Sports Med 1988;16:170-80.
11. Snyder-Mackler L, Ladin Z, Schepsis AA, Young JC. Electrical
stimulation of the thigh muscles after reconstruction of the anterior
cruciate ligament. Effects of electrically elicited contraction of the
quadriceps femoris and hamstring muscles on gait and on strength of the
thigh muscles. 1991;73-A:1025-36.
12. Snyder-Mackler L, De Luca PF, Williams PR, Eastlack ME,
Bartolozzi AR, III. Reflex inhibition of the quadriceps femoris muscle
after injury or reconstruction of the anterior cruciate ligament. 1994;76-A:555-60.
13. Tibone JE, Antich TJ. A biomechanical analysis of anterior
cruciate ligament reconstruction with the patellar tendon. A two year
followup. Am J Sports Med 1988;16:332-5.
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