As the area of the hernia defect (measured clinically) increased, there was a proportional decrease in abdominal wall muscle strength (as Nm force). The abdominal wall muscle strength prior to the laparotomy resulting in the hernia was unknown. Even so, the correlation between hernia area measured clinically and decrease in abdominal muscle strength in all BioDex modalities is so robust that it seems safe to conclude that the area of the hernia is an important determinant for the degree of function lost. Indirectly, this also indicates those patients who will benefit most from surgery, and perhaps those who should not wait until their hernia defect progresses to a giant hernia. Measurement of hernia size is taken as either the length and /or width of the defect or the area. However, the area may be the most important predictor of clinical outcome. In this study, all BioDex forces measured during flexion, extension and isometric contraction, showed a strong inverse relationship to the hernia area determined from clinical measurements. One could have expected only the force of isometric contraction to be inversely proportional to the area since previous studies have shown that patients with a giant hernia have more pronounced difficulty in performing exercises involving movements of extension/flexion . This may be due to a reduction in their capacity to perform repetitive movements as opposed to isometric contraction where there is a constant strain but no movement. On the contrary Criss et al showed improvement in both flexion and extension work load after abdominal hernia repair . Criss also showed that all 13 of his patients showed an improvement in quality-of-life measured with HerQles, a validated questionnaire . This is an important improvement and needs further investigation. It is difficult to design objective methods to determine the strength of the abdominal wall. Curl-ups have been tested  but this method is hard to reproduce. The BioDex system is probably the most precise and reproducible method to measure abdominal muscle strength, though only the combined strength of all muscles is measured [7, 8]. Testing could be further improved if EMG is added.
BMI, gender and age were not correlated to abdominal wall muscle strength. Thus no multivariate analyses, for example linear regression analysis, were performed.
At present it is not possible to determine which patients will benefit most from surgical hernia repair and many aspects must be considered before deciding on surgery. Important aspects include the risk for serious adverse effects emanating from synthetic reinforcement material, abdominal pain after surgery, and other risks related to anaesthesia and surgery . It is thus of paramount importance to assess patient satisfaction using, for instance, a questionnaire as one PROM regarding pain related to function [14–16] as well as objective functional measurements such as muscle strength measured by the BioDex system before deciding on surgery.
It could be hypothesized that preoperative pain from a giant hernia may result in weak abdominal muscles and resulting back pain. These patients have difficulty in performing sports due to both a high BMI and spatial limitations from their giant hernia. It is well known that patients with inguinal hernia and pain before surgery are more prone to suffer from long-term postoperative pain. It is still not known if this is also true for giant ventral hernia, and this is an important field of research. At present there is only one study suggesting that patients with pain from ventral hernia are more prone to develop long-term pain after surgery . If such a relationship is confirmed for giant ventral hernia, it would suggest that these patients should be operated as soon as the hernia causes the patient problems, not waiting until pain arises from weak abdominal muscle strength, or until incarceration or other imperative symptoms occur.
It is a matter of debate as to which ventral hernias require surgery, and when. Small hernias are usually repaired due to the high risk for incarceration of the intestine. In contrast, surgery for giant ventral hernia has a high complication rate including the risk for difficulty in breathing and disturbance of wound healing. Small hernias, less than 15 mm, may be sutured without the application of a mesh, while giant hernia repair requires some form of reinforcement [1, 18]. den Hartog showed improved muscle strength after suture repair compared to laparoscopic repair with mesh, but the size of the hernias was not given . It can also be hypothesized that some hernia patients may have impaired muscle strength due to an imbalance in ECM formation or remodeling capacity, resulting in weaker collagen and stroma structures, a status that also predisposes to hernia. Several factors are involved in ECM remodeling including a series of zinc- dependent matrix metalloproteinases (MMPs). Antoniou et al demonstrated in 2011 that local tissue levels of MMP-2 and -9 were increased while systemic levels of the same MMPs were decreased in most patients with inguinal hernia . Moreover, an imbalance between collagen I/III and MMP 1 has been shown to predispose to hernia . It is possible that such patients are more likely to benefit from surgery, and that monitoring the levels of both local and circulating MMPs may improve patient selection. However, this remains to be seen.
Hernia patients often receive contradictory advice regarding physical activity. In the case of giant ventral hernia it is still an open question whether exercise of the abdominal wall muscles leads to greater diastasis or whether it is possible to increase muscle mass thereby bringing these muscles together. In patients suffering from diastasis recti it has been shown that the width of the Linea Alba can be reduced by exercise . When including active training in the work-up prior to surgery, close collaboration with an involved physiotherapist is important to avoid any side effects of muscle exercise.
An interesting observation in the present study was that the hernia area determined by CT scan showed no correlation to abdominal muscle strength. Width of abdominal rectus diastasis by CT scan has previously been shown not to correspond to that measured clinically, the latter more closely representing the “truth” found at surgery . One could speculate that muscle fibers identified by the CT scan represent all fibers, regardless of whether they are functional or largely consist of fibrous tissue. Clinical evaluation, on the other hand, probably only takes into account muscles with the capacity to contract on demand. Should this be the case, the lack of correlation between hernia area measured by CT scan and abdominal muscle strength, seen in this study, would seem logical. There was no evaluation of inter-rater reliability included in the present study; the length and width of the hernia was requested at the original radiological investigation on admission. A previous study has shown a high degree of inter-rater reliability when determining the width of the diastasis between the rectus muscles from CT scans . CT scanning, however, remains an essential investigation in the preoperative assessment of patients suffering from a ventral hernia; not for an exact evaluation of the size of the abdominal wall defect, but to detect associated pathology and for assistance in the planning of the surgical procedure.
A large prospective study measuring preoperative abdominal wall muscle strength is required to see if patients who develop a giant hernia also had weaker abdominal muscles prior to the index abdominal operation causing the hernia. Furthermore, a study on local MMP levels in muscle and fascia biopsies as well as systemic levels, in patients with a hernia may give more insight into the pathogenesis of this disorder.